The Earth’s atmosphere is composed of about 77 percent nitrogen, 21 percent oxygen, and traces of argon, carbon dioxide, water, and other compounds and elements. It is interesting that the Earth maintains free oxygen, as it is a very reactive gas. Under most circumstances, it combines readily with other elements. But our atmosphere’s oxygen is pro- 17 duced because of biological processes. Without life on Earth, there would be no free oxygen in our atmosphere.
When the Earth formed, it is believed
that the atmosphere contained a much
larger amount of carbon dioxide-perhaps
as much as 80 percent-but this diminished to about 20 to 30 percent over the
next 2.5 billion years. Since that time, the
gas has been incorporated into carbonate
rocks, and to a lesser extent, dissolved into
the oceans and consumed by living organisms, especially plants. Today, the movement of the continental plates, the
exchange of gas between the atmosphere
and the ocean’s surface, and biological
processes (such as plant respiration) help
continue the complex carbon dioxide flow,
keeping the amount of carbon dioxide in balance.
Georgius Agricola, whose real name was Georg Bauer, was a German scholar and scientist who is often considered one of the founding figures of modern mineralogy and the father of the field of geology. He was born on March 24, 1494, in Glauchau, Saxony (now part of Germany), and died on November 21, 1555, in Chemnitz, Saxony.
Georgius Agricola
Agricola is best known for his work “De re metallica,” which was published posthumously in 1556. This comprehensive treatise on mining and metallurgy is considered one of the most important works on the subject during the Renaissance. It described various mining and metallurgical techniques used in his time and included detailed illustrations and descriptions of mining equipment, smelting processes, and mineral deposits.
In addition to his work on mining and metallurgy, Agricola made significant contributions to the fields of mineralogy, geology, and the natural sciences. He emphasized the importance of careful observation and classification of minerals and rocks and laid the groundwork for the systematic study of Earth’s crust.
Agricola’s work had a lasting impact on the development of these fields, and he is often regarded as one of the pioneers of the Earth sciences. His contributions to the understanding of minerals, rocks, and mining practices played a crucial role in the advancement of geology and metallurgy in the centuries that followed.
Stratigraphyis a branch of geology to description of rock or interpretation geologic time scale.It provides of geologic history of strata. Stratigraphic studies primarily used in the study of sedimentary and volcanic layered rocks.
Two type related subfields
Lithologic Stratigraphy Or Lithostratigraphy
Biologic Stratigraphy Or Biostratigraphy
A not unusual purpose of stratigraphic studies is the subdivision of a series of rock strata into mappable gadgets, figuring out the time relationships that are involved, and correlating devices of the sequence—or the complete sequence—with rock strata elsewhere. Following the failed attempts over the last half of the 19th century of the International Geological Congress (IGC; based 1878) to standardize a stratigraphic scale, the International Union of Geological Sciences (IUGS; based 1961) mounted a Commission on Stratigraphy to paintings closer to that cease. Traditional stratigraphic schemes depend upon scales: (1) a time scale (using eons, eras, durations, epochs, a while, and chrons), for which every unit is described by means of its beginning and finishing factors, and (2) a correlated scale of rock sequences (using structures, series, tiers, and chronozones). These schemes, whilst used in conjunction with different relationship strategies—along with radiometric courting (the measurement of radioactive decay), paleoclimatic dating, and paleomagnetic determinations—that, in general, had been advanced within the closing 1/2 of the 20th century, have caused particularly less confusion of nomenclature and to ever more dependable data on which to base conclusions about Earth history.
Because oil and natural gasoline nearly always arise in stratified sedimentary rocks, the process of locating petroleum reservoir traps has been facilitated notably with the aid of using stratigraphic standards and information.
An crucial principle in the software of stratigraphy to archaeology is the law of superposition—the principle that in any undisturbed deposit the oldest layers are normally placed at the bottom degree. Accordingly, it is presumed that the remains of every succeeding era are left at the debris of the last.
Lithostratigraphy is associated with the study of strata (layer).In general a stratum is sedimentary or igneous rock related to formed of rock
Types of lithostratigraphic units
A lithostratigraphic unit conforms to the regulation of superposition, which state that during any succession of strata, not disturbed or overturned for the reason that deposition, younger rocks lies above older rocks. The precept of lateral continuity states that a fixed of mattress extends and can be traceable over a huge region.
Lithostratigraphic devices are identified and defined on the idea of observable rock characteristics. The descriptions of strata based totally on bodily look define facies. Lithostratigraphic devices are most effective described by way of lithic traits, and no longer by using age.
Stratotype: A designated sort of unit inclusive of handy rocks that include straight forward characteristics which might be consultant of a selected lithostratigraphic unit.
Lithosome: Masses of rock of essentially uniform man or woman and having interchanging relationships with adjoining hundreds of different lithology. E.G.: shale lithosome, limestone lithosome.
The essential Lithostratigraphic unit is the formation. A formation is a lithologically extraordinary stratigraphic unit this is massive enough to be mappable and traceable. Formations may be subdivided into individuals and beds and aggregated with different formations into organizations and supergroups.
Stratigraphic relationship
Two types of contact: conformable and unconformable.
Conformable: unbroken deposition, no break or hiatus (break or interruption in the continuity of the geological record). The surface strata resulting is called a conformity.
Two types of contact between conformable strata: abrupt contacts (directly separate beds of distinctly different lithology, minor depositional break, called diastems) and gradational contact (gradual change in deposition, mixing zone).
Unconformable: period of erosion/non-deposition. The surface stratum resulting is called an unconformity.
Angular unconformity: younger sediment lies upon an eroded surface of tilted or folded older rocks. The older rock dips at a different angle from the younger.
Disconformity: the contact between younger and older beds is marked by visible, irregular erosional surfaces. Paleosol might develop right above the disconformity surface because of the non-deposition setting.
Paraconformity: the bedding planes below and above the unconformity are parallel. A time gap is present, as shown by a faunal break, but there is no erosion, just a period of non-deposition.
Nonconformity: relatively young sediments are deposited right above older igneous or metamorphic rocks.
Biostratigraphy
Biostratigraphy is the department of stratigraphy which makes a speciality of correlating and assigning relative a while of rock strata by the use of the fossil assemblages contained inside them. Usually the purpose is correlation, demonstrating that a particular horizon in a single geological section represents the identical time period as another horizon at some other phase. The fossils are useful because sediments of the equal age can appearance absolutely special due to local versions in the sedimentary environment. For instance, one segment could have been made up of clays and marls while any other has greater chalky limestones, however if the fossil species recorded are similar, the two sediments are likely to were laid down at the same time.
Stratigraphic Subdivision
Concept of stage
A stage is a major subdivision of strata, each systematically following the other each bearing a unique assemblage of fossils. Therefore, stages can be defined as a group of strata containing the same major fossil assemblages. French palaeontologist Alcide d’Orbigny is credited for the invention of this concept. He named stages after geographic localities with particularly good sections of rock strata that bear the characteristic fossils on which the stages are based.
Concept of zone
The zone is the fundamental biostratigraphic unit. Its thickness range from a few to hundreds of metres, and its extant range from local to worldwide. Biostratigraphic units are divided into six principal kinds of biozones:
Taxon range biozone represent the known stratigraphic and geographic range of occurrence of a single taxon.
Concurrent range biozone include the concurrent, coincident, or overlapping part of the range of two specified taxa.
Interval biozone include the strata between two specific biostratigraphic surfaces. It can be based on lowest or highest occurrences.
Lineage biozone are strata containing species representing a specific segment of an evolutionary lineage.
Assemblage biozones are strata that contain a unique association of three or more taxa.
Abundance biozone are strata in which the abundance of a particular taxon or group of taxa is significantly greater than in the adjacent part of the section.
Index fossils
To be useful in stratigraphic correlation index fossils should be:
Independent of their environment
Geographically widespread (provincialism/isolation of species should be avoided as much as possible)
Rapidly evolving
Abundant (easy to find in the rock record)
Easy to preserve (Easier in low-energy, non-oxidized environment)
Although the science of geology as we know it today is a relatively young field, insightful observations of Earth processes were made as far back as the ancient Greeks. Some of these early ideas were handed down through the ages. For example, Herodotus (c. 484-425? B.LE.) had rather modern insights about the formation of the Nile River delta and the important role sediment (deposited by flooding) played in producing the fertile Nile Valley. The Greek historian also applied a primitive form of a principle known as uniformitarianism, the idea that existing processes are sufficient to explain all geological changes that have occurred over time. But many other “geological” observations by the ancient Greeks seem fanciful today. Por example, Aristotle (384-322 H.C.E.), the famous philosopher and tutor to Alexander the Great, believed that the heat from volcanic eruptions was produced by underground fires. He also believed that air moving through caverns became heated by friction, causing these fires.
Geology is a vast field, stretching from paleontology to mineralogy. It is easy to see why, since there are so many features and processes taking place on the Earth and beyond. The following lists some important subdivisions of geology
Economic geology-the study of how rocks are used, mined, bought, and sold, such as in the search for metals. In other words, economic geologists explore our natural resources and their development.
Environmental geology-the study of the environmental effects produced by changes in geology, such as the determination river flow and its connection to flooding, and conversely, how the geology is affected by environmental problems, such as pollution and urban development.
Geochemistry-the study of the chemical composition of rocks and minerals; geochemists use this information to determine more about the internal structure of materials.
Geomorpholoqy-the study of landform development, such as how a river forms and develops over time.
Geophysics-the physics of the Earth, including such fields as seismology (including interpretation of the Earth’s interior), and the effects of the Earth’s magnetic and electric fields.
Glacial Geoloqy-how ice sheets and glaciers affect each other and the geology of an area.
Hydrology-how water, such as groundwater flow in a karst terrain or how pollution moves underground, affects the geology of an area.
Limno qeology-the study of ancient and modern lakes.
Marine geology-the study of the geology of the ocean floor and/or coastline, especially with regard to how they change over time.
Paleontoloqy-the study of ancient life in the form of fossils, including specializations in invertebrates, vertebrates, plants, and dinosaurs.
Petroleum geology-the study of how petroleum products are formed, found, and extracted.
Planetology-the study of the planets and satellites of our solar system, especially with regard to their formation and how they compare to the Earth.
Soapstone is a type of talc-schist metamorphic rock. Also other naming’s are steatite or soaprock. The composed primarily of talc, with varying amount of micas, chlorite, amphiboles, carbonates and other minerals. It is produced by dynamothermal metamorphism and metasomatism. It occurs in the regions where tectonic plates are present, replacing the rocks with heat and pressure, with the flow of liquids, but without melting. It has been an environment for carving for thousands of years. It is composed primarily of talc so it usually very soft. It is typically gray, bluish, green, or brown in color, often variegated. Its name is derived from its “soapy” feel and softness.
Soapstone Rock Hand specimen The outer layers of the Redeemer sculpture made of soapstone.
Texture: Non-foliated
to weakly-foliated; Fine-grained
Metamorphic
Environment: Hydrothermal solutions concentrated during final stages of
magma crystallization in batholiths or hot seawater solutions drawn down into
subduction zones
Hardness: Very
soft because of primary mineral is talc
Soapstone composed is predominantly talc and various amounts
of chlorite and amphiboles (typically tremolite, anthophyllite and
cummingtonite) and traces of small iron-chromium oxide. It may be schistose or
massive. Soapstone is formed by metamorphism of ultramafic protoliths (eg
dunite or serpentinite) and metasomatism of siliceous dolomites.
By mass, “pure” steatite is roughly 63.37% silica,
31.88% magnesia, and 4.74% water. It commonly contains minor quantities of
other oxides such as CaO or Al2O3.
Soapstone Formation
Soapstone is a metamorphic rock that forms through the metamorphism of magnesium-rich rocks, primarily ultramafic rocks such as peridotite and pyroxenite. The formation of soapstone involves changes in temperature, pressure, and mineral composition over time. Here’s a brief overview of the process of soapstone formation:
Protolith Formation: The process begins with the formation of the protolith, which is the original parent rock from which soapstone will develop. This protolith is usually an ultramafic rock, rich in minerals like olivine, pyroxenes, and serpentine minerals.
Metamorphism: Metamorphism is the process by which the protolith undergoes changes in response to increased temperature and pressure. In the case of soapstone, low to moderate metamorphic conditions are essential. The exact conditions can vary, but they typically involve temperatures between 400°C and 800°C and pressures of 1 to 2 kilobars.
Hydration and Serpentinization: One of the key processes during the metamorphism of the protolith is hydration, particularly serpentinization. Serpentinization involves the transformation of minerals like olivine and pyroxenes into serpentine minerals due to the introduction of water into the rock. Serpentine minerals, such as antigorite and lizardite, are rich in magnesium and contribute to soapstone’s characteristic softness and texture.
Formation of Talc: As the ultramafic rock undergoes serpentinization, some of the serpentine minerals can further transform into talc through additional chemical reactions. Talc is a soft mineral composed mainly of magnesium, silicon, and oxygen. The presence of talc is a defining characteristic of soapstone and gives the rock its unique properties.
Mineral Recrystallization and Texture: During metamorphism, the minerals in the protolith recrystallize, resulting in a fine-grained texture in the soapstone. The new mineral crystals, including talc and other metamorphic minerals, are typically interlocking and give the rock its characteristic appearance.
Regional and Contact Metamorphism: Soapstone can form through both regional and contact metamorphism. Regional metamorphism occurs over large areas due to tectonic forces and is responsible for the development of large soapstone deposits. Contact metamorphism occurs when rocks come into direct contact with hot magma, leading to localized changes and the formation of smaller soapstone occurrences.
In summary, soapstone formation involves the metamorphism of magnesium-rich ultramafic rocks, primarily through processes like hydration, serpentinization, and mineral recrystallization. The presence of talc and other metamorphic minerals gives soapstone its distinctive properties, including its softness, heat resistance, and characteristic texture.
Where is it found?
Soapstone Distribution
Soapstone is found in various locations around the world, often associated with regions where metamorphic processes have occurred and where suitable parent rocks (such as ultramafic rocks) are present. Some of the notable regions where soapstone is found include:
United States: Soapstone deposits are found in several states, including Vermont, Virginia, North Carolina, Georgia, and California. Vermont is particularly famous for its high-quality soapstone used in carvings, countertops, and other applications.
Brazil: Brazil is a significant producer of soapstone, with deposits located in the state of Minas Gerais. Brazilian soapstone is known for its diverse range of colors and is commonly used for sculptures and other artistic creations.
India: India is another major producer of soapstone, with deposits located in the states of Rajasthan, Uttar Pradesh, and Andhra Pradesh. Indian soapstone is used for a wide range of purposes, including carvings, kitchenware, and architectural elements.
Finland: Soapstone is found in various regions of Finland, where it is known as “spekstone.” Finnish soapstone has been historically used for stoves and fireplaces due to its excellent heat retention properties.
Canada: Soapstone deposits can be found in parts of Canada, including Quebec and Ontario. Canadian soapstone has been used by indigenous peoples for carvings and artwork.
China: Soapstone is found in various provinces in China, and Chinese soapstone carvings have a long history in traditional art.
Kenya: Soapstone deposits are found in the Kisii region of Kenya, and local artisans create intricate carvings and sculptures from this stone.
Peru: Soapstone deposits are found in the Andes Mountains of Peru, where it has been used by indigenous cultures for centuries.
Pakistan: Soapstone deposits are found in regions like Khyber Pakhtunkhwa and Balochistan in Pakistan.
These are just a few examples, and soapstone can be found in other countries as well. The specific colors, qualities, and uses of soapstone can vary depending on the location. It’s important to note that soapstone quarries and deposits can sometimes be localized, and the availability of specific types of soapstone may vary from region to region.
Soapstone Characteristics and Properties
Soapstone Characteristics and Properties
Soapstone is a unique metamorphic rock known for its distinct characteristics and properties. Here are some key features that define soapstone:
Texture and Appearance:
Soapstone has a smooth, soapy feel to the touch, which gives it its name.
It often has a medium to fine-grained texture due to the recrystallization of minerals during metamorphism.
The color of soapstone varies and can range from light gray to bluish, greenish, or even black. Some varieties exhibit veining or mottling.
Softness:
One of the most notable properties of soapstone is its softness. It is relatively easy to carve and shape using simple tools, which makes it a preferred material for sculptures and carvings.
Mineral Composition:
Soapstone primarily consists of talc, which is a soft mineral composed of magnesium, silicon, and oxygen.
It may also contain other minerals like chlorite, pyroxenes, amphiboles, micas, and carbonates, depending on the specific composition of the parent rock and the metamorphic process.
Heat Resistance and Thermal Properties:
Soapstone has excellent heat retention properties. It can absorb, store, and radiate heat over an extended period, making it suitable for stoves, fireplaces, and cookware.
Due to its ability to withstand high temperatures, it is often used for countertops and surfaces in kitchens and laboratories.
Chemical Stability:
Soapstone is chemically inert and does not react with acids or alkalis, which contributes to its durability and resistance to weathering.
Density and Hardness:
Soapstone is relatively low in density and hardness compared to many other rocks. It is softer than minerals like quartz and feldspar and can be easily scratched with a fingernail or a metal object.
Sculptural and Carving Qualities:
The softness and ease of carving make soapstone a favored material for sculptures, ornaments, and decorative objects.
Artisans appreciate soapstone for its workability and the way it holds intricate details.
Architectural and Design Applications:
Soapstone is used for architectural elements such as countertops, sinks, vanities, and flooring tiles due to its aesthetic appeal, heat resistance, and chemical stability.
Its smooth texture and natural beauty make it a popular choice for both traditional and contemporary designs.
Sound Absorption:
Soapstone has acoustic properties that make it useful for sound absorption. It is sometimes used in architectural settings to reduce noise and enhance acoustics.
Variability:
The properties of soapstone can vary depending on its mineral composition, location of formation, and specific metamorphic conditions.
Overall, soapstone’s unique combination of properties makes it a versatile and sought-after material for a wide range of artistic, architectural, and practical applications.
Applications and Uses
Soapstone Applications and Uses
Soapstone has a wide range of applications and uses due to its unique properties and characteristics. Its versatility, heat resistance, and workability make it suitable for both artistic and practical purposes. Here are some common applications and uses of soapstone:
Sculptures and Carvings:
Soapstone’s softness and ease of carving make it a favored material for sculptors and artisans to create intricate and detailed sculptures, figurines, and ornaments.
Countertops and Surfaces:
Soapstone is used for kitchen and bathroom countertops due to its natural beauty, heat resistance, and durability. It provides a unique and elegant look to interior spaces.
Fireplaces and Wood Stoves:
Soapstone’s excellent heat retention properties make it an ideal material for constructing fireplaces, wood-burning stoves, and hearths. It can radiate heat even after the fire has gone out.
Cookware and Baking Stones:
Soapstone’s ability to absorb and evenly distribute heat makes it suitable for cookware such as baking stones, pizza stones, and griddles.
Sinks and Vanity Tops:
Soapstone is used to create sinks, vanity tops, and bathroom fixtures due to its resistance to water and chemicals.
Laboratories and Science Settings:
Soapstone’s chemical stability and heat resistance make it suitable for laboratory countertops, tabletops, and work surfaces.
Architectural Elements:
Soapstone is used for architectural details, such as window sills, stair treads, wall cladding, and flooring tiles, adding a touch of elegance and natural beauty to buildings.
Art and Crafts:
In addition to sculptures, soapstone is used in various forms of artistic expression, including relief carvings, decorative boxes, and jewelry.
Aesthetic and Decorative Purposes:
Soapstone’s unique color variations and smooth texture make it appealing for decorative items such as vases, coasters, candle holders, and bookends.
Acoustic Panels and Absorption:
Due to its sound-absorbing properties, soapstone is used in acoustic panels, recording studios, and theaters to improve sound quality and reduce echo.
Historical and Cultural Artifacts:
Indigenous cultures have historically used soapstone for traditional carvings, tools, and cultural artifacts.
Eco-Friendly and Sustainable Products:
Soapstone is often considered an environmentally friendly choice for countertops and other surfaces due to its natural abundance, long lifespan, and potential for recycling.
It’s important to note that the specific uses of soapstone can vary depending on the region, local traditions, and availability. Its versatility and aesthetic appeal have made it a valued material across cultures and throughout history.
Conclusion
It is primarily made of talc. It shares many physical properties with this mineral and makes it valuable for many different uses. It is non-porous, heat resistant, non-absorbent, soft and easy to process, high specific heat capacity, resistant to acids and bases.
The mineral composition of this rock may vary. It depends on the main rock material and the pressure / temperature conditions of the metamorphic environment.
Grain size is determined by the level of metamorphism. There are more durable hard varieties used in machine construction, and some have the desired fine particle size for high carvings.
8,000 years ago, Native Americans used the rock to make carved sculptures and cooking pots. In the Late Archaic Period, Native Americans from North America made bowls, smoking pipes, cooking plates and ornaments.
During the Stone Age, the people of Scandinavia used molded patterns of soapstone to pour metal objects such as knife blades and spearheads. They discovered that they were able to heat the soapstone and then spread it slowly. This causes them to make cooking utensils, bowls, cooker liners and cooking plates from soapstone.
The famous sculpture of the city of Rio de Janeiro, which overlooks the “Savior Christ”, is made of concrete and is faced with soapstone. It weighs 635 mt and stands at a height of 120 feet. The sculpture was founded between 1922 and 1931. It has become a cultural symbol.
During the Revolutionary War, the army removed the molds from the soap molds because they were easily carved and heat resistant.
Its electrical properties are used as an insulator for the body and electrical components due to its durability and can be pressed in complex shapes before firing.
As an alternative natural stone kitchen counter instead of marble or granite, soapstone is often used because it is not stained with tomatoes, grape juice or wine. It is used in laboratories because it is not affected by acids and bases. Soapstone is not affected by heat, so a casserole can be placed on it without fear of burning or damaging the surface.
Soapstone is applied to almost every object, mainly made of talc, leaving a white trace. Tailors, carpenters and other artisans use soap stones because they have been using soapstone as a marking tool for years. It is also used as a marker by welders during welding, because the powder is heat resistant and does not burn.
Small chilled soapstone can be used instead of ice in a glass of whiskey. It is ideal because it does not dilute the alcohol and a few stones can keep a drink cold for more than 30 minutes because the temperature of the rock changes very slowly. Also because the rock is soft, it does not scratch the glass.
References
Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
Clark, Sarah. (2017, April 24). The Characteristics of Slate. Sciencing. Retrieved from https://sciencing.com/characteristics-slate-8199338.html
Volcanic bomb is pyroclastic rock that is a cooling of a mass of lava it flies thorough the air after eruption. If it is to be called a bomb, a specimens must be larger than 2, 5 inch diameter. Smaller specimens are known as Lapilli. Specimens up to 20 ft. (6 m) in diameter are known. Volcanic bombs are usually brown or red, weathering to a yellow-brown color. Specimens can become rounded as they fly through the air, although they may also be twisted or pointed. They may have a cracked, fine-grained, or glassy surface. There are several types of volcanic bomb, which are named according to their outward appearance and structure.
Color: Dark
shades of red, brown, or green
Group: Extrusive
Minerals: Volcanic bombs commonly possess a basaltic or similar mafic composition.
Bombs are named according to their shape, which is
determined by the fluidity of the magma from which they are formed.
Ribbon or cylindrical
bombs form from highly to moderately fluid magma, ejected as irregular
strings and blobs. The strings break up into small segments which fall to the
ground intact and look like ribbons. Hence, the name “ribbon bombs”.
These bombs are circular or flattened in cross section, are fluted along their
length, and have tabular vesicles.
Spherical bombs
also form from high to moderately fluid magma. In the case of spherical bombs,
surface tension plays a major role in pulling the ejecta into spheres.
Spindle, fusiform, or
almond/rotational bombs are formed by the same processes as spherical
bombs, though the major difference being the partial nature of the spherical
shape. Spinning during flight leaves these bombs looking elongated or almond
shaped; the spinning theory behind these bombs’ development has also given them
the name ‘fusiform bombs’. Spindle bombs are characterized by longitudinal
fluting, one side slightly smoother and broader than the other. This smooth
side represents the underside of the bomb as it fell through the air.
Cow pie bombs are
formed when highly fluid magma falls from moderate height, so the bombs do not
solidify before impact (they are still liquid when they strike the ground).
They consequently flatten or splash and form irregular roundish disks, which
resemble cow dung.
Bread-crust bombs
are formed if the outside of the lava bombs solidifies during their flights. They
may develop cracked outer surfaces as the interiors continue to expand.
Cored bombs are
bombs that have rinds of lava enclosing a core of previously consolidated lava.
The core consists of accessory fragments of an earlier eruption, accidental
fragments of country rock or, in rare cases, bits of lava formed earlier during
the same eruption.
Volcanic Bomb Formation
A volcanic bomb is a type of volcanic projectile that forms during explosive eruptions. It is typically a rounded to elongated mass of molten rock (lava) that is ejected from a volcano while still semi-liquid or plastic. Volcanic bombs can vary in size from a few centimeters to several meters in diameter, and they can travel significant distances away from the vent of the volcano before landing.
The formation of volcanic bombs involves a combination of processes related to the nature of the erupting magma and the explosive dynamics of the eruption itself. Here’s an overview of how volcanic bombs form:
Magma Composition: The composition of the magma plays a crucial role in the formation of volcanic bombs. The magma needs to be sufficiently viscous (thick and sticky) to resist fragmentation into small particles during the eruption. This viscosity is often influenced by factors such as the silica content of the magma.
Gas Content: Magma contains dissolved gases, primarily water vapor and carbon dioxide. As the magma rises toward the surface, the decreasing pressure allows these dissolved gases to come out of solution and form bubbles. The accumulation of gas bubbles within the magma increases its internal pressure.
Explosive Eruption: During an explosive volcanic eruption, the pressure from the expanding gas bubbles within the magma becomes significant. When this pressure exceeds the strength of the surrounding rock, it can lead to the fragmentation of the magma into smaller particles, forming a mixture of fragmented lava, volcanic ash, and gases known as a pyroclastic flow or pyroclastic surge.
Ejection of Molten Fragments: In addition to the fine ash and rock fragments, larger, semi-liquid or plastic globs of magma can also be expelled from the vent. These globs are volcanic bombs. The bombs are often shaped by their aerodynamic interaction with the surrounding air as they are ejected, which can give them a characteristic streamlined or teardrop shape.
Solidification: As volcanic bombs are expelled into the atmosphere, they start to cool rapidly due to the lower temperature at higher altitudes. The outer layer of the bomb solidifies, forming a crust, while the interior remains partially molten. This can create a distinctive “bread crust” appearance.
Landing: The solidified outer crust of the bomb helps it retain its shape as it travels through the air and lands on the ground. Depending on the size, shape, and initial velocity of the bomb, it may either bury itself partially or completely in the ground or create impact craters upon landing.
In summary, volcanic bombs form during explosive volcanic eruptions when semi-liquid or plastic magma is ejected from the vent due to the buildup of gas pressure. The bombs cool and solidify as they travel through the air before landing on the ground, often displaying distinctive shapes and textures due to their aerodynamic interactions and rapid cooling.
Volcanic Bomb Distribution Area
The distribution area of volcanic bombs, or the area where they can be found after being ejected from a volcano during an eruption, can vary widely depending on several factors. These factors include the type of eruption, the size of the volcano, the type of magma involved, prevailing wind conditions, and the strength of the explosive event. Here are some general considerations for the distribution area of volcanic bombs:
Eruption Type: Different types of volcanic eruptions can lead to varying distributions of volcanic bombs. Explosive eruptions, such as Plinian or Vulcanian eruptions, are more likely to eject volcanic bombs over larger distances compared to effusive eruptions, where lava flows out relatively gently.
Volcano Size: Larger volcanoes tend to have greater explosive potential, which can result in the ejection of volcanic bombs over larger areas. Smaller volcanoes might have more localized distributions.
Magma Properties: The viscosity and gas content of the magma play a significant role. More viscous magmas are more likely to form volcanic bombs and can carry them greater distances due to their resistance to fragmentation.
Wind Patterns: Prevailing wind patterns at the time of eruption can carry volcanic bombs in specific directions. Wind can greatly influence the distribution area, potentially carrying volcanic bombs far downwind from the eruptive vent.
Eruption Intensity: The intensity of the eruption, including factors like the height of the eruption column, the rate of magma discharge, and the explosiveness of the event, can influence how far volcanic bombs are ejected.
Topography: The local terrain and topography can affect the distribution of volcanic bombs. Mountains, hills, and valleys can deflect or funnel the trajectory of ejected material.
Geographical Location: The location of the volcano, its proximity to populated areas, and the presence of natural barriers can influence where volcanic bombs are distributed.
Eruption History: Previous eruptions of the same volcano can provide insight into the potential distribution area of volcanic bombs. Patterns from past eruptions may be used to estimate the range of distribution for future events.
It’s important to note that while volcanic bombs can travel significant distances from the eruptive vent, they are often found closer to the volcano itself. The distribution area can extend from the immediate vicinity of the vent to several kilometers away, depending on the factors mentioned above.
Researchers and volcanologists often study the distribution of volcanic bombs and other volcanic ejecta to gain a better understanding of the eruptive processes and hazards associated with volcanic activity. This information can be crucial for hazard assessment and risk mitigation in volcanic regions.
Physical Properties of Volcanic Bombs
Physical Properties of Volcanic Bombs
The physical properties of volcanic bombs are influenced by their formation, flight through the air, and subsequent cooling and solidification processes. Here are the key physical properties of volcanic bombs:
Shape and Size: Volcanic bombs can exhibit a wide range of shapes and sizes. Their forms can include spherical, elliptical, streamlined, or irregular shapes, depending on their aerodynamic interaction with the air during flight. Sizes can vary from centimeters to several meters in diameter, with larger bombs often having elongated or teardrop shapes.
Exterior Crust: As volcanic bombs are ejected from the volcano and travel through the air, their outer layers cool and solidify rapidly due to exposure to lower temperatures at higher altitudes. This results in the formation of a solid crust on the surface of the bomb. The exterior crust can be rough or smooth and is often darker in color compared to the molten interior.
Interior Texture: The interior of a volcanic bomb may remain partially molten or contain pockets of semi-molten material. The interior texture can range from glassy or crystalline to vesicular (containing gas bubbles) depending on the cooling rate and the mineral composition of the magma.
Vesicles: Many volcanic bombs contain vesicles, which are small gas bubbles that were present in the molten magma before ejection. These vesicles often collapse or partially close as the bomb cools and solidifies, leaving voids or cavities in the interior.
Weight and Density: The weight and density of a volcanic bomb are determined by its size, shape, and composition. Larger bombs tend to have greater mass and density. The crust of the bomb contributes to its overall weight and density, while the vesicles may reduce overall density.
Impact Features: When volcanic bombs land, they can create impact craters or depressions in the ground due to their kinetic energy upon impact. The shape and depth of these features can provide insights into the angle of impact and the velocity of the bomb.
Color: The color of volcanic bombs can vary based on the mineral composition of the magma. Bombs may be dark-colored if they contain iron-rich minerals or lighter-colored if they have a higher proportion of silicate minerals.
Surface Features: The exterior surface of a volcanic bomb can exhibit various features, including flow lines, grooves, and ridges. These features result from the bomb’s interaction with the air and its rotational motion during flight.
Cooling Rate: The rate at which a volcanic bomb cools influences its internal crystallinity and texture. Rapid cooling at the surface may lead to a glassy texture, while slower cooling in the interior can promote the growth of crystals.
Understanding the physical properties of volcanic bombs provides valuable information about the eruption dynamics, magma behavior, and volcanic processes. These properties can be studied to decipher the conditions under which the bombs formed and traveled through the atmosphere before landing, contributing to our knowledge of volcanic hazards and eruption mechanisms.
References
Bonewitz, R. (2012). Rocks and minerals. 2nd ed.
London: DK Publishing.
Wikipedia contributors. (2018, October 18).
Volcanic bomb. In Wikipedia, The Free Encyclopedia. Retrieved 15:22, May 14,
2019, from
https://en.wikipedia.org/w/index.php?title=Volcanic_bomb&oldid=864612411
Agglomerate rock is a type of sedimentary rock that forms through the accumulation and cementation of coarse fragments of various sizes, typically ranging from gravel to larger boulders. It is considered a conglomerate rock, which is a category of sedimentary rocks characterized by the presence of rounded or angular clasts (rock fragments) that are bound together by a matrix of finer-grained material. Agglomerate rocks are primarily composed of clasts that are larger than 2 millimeters in diameter.
Agglomerate is a pyroclastic coarse accumulation of blocks of volcanic metarial that contains atl least 75% bombs, rounded clasts in a matriix of lava or ash. The clasts are fragments particles that may be derived from, country rock or pyroclastic rocks.
Name origin: The name derived from the Latin agglomerare meaning
“to form into a ball
Composition: Agglomerate rocks consist of three main components:
Clasts: These are the larger rock fragments or particles that make up the bulk of the rock. Clasts in agglomerate rocks can be made of a variety of materials, such as different types of rocks, minerals, and even volcanic material like pumice or basalt. These clasts are typically angular or rounded, depending on the processes that shaped and transported them.
Matrix: The matrix is the finer-grained material that fills the spaces between the clasts and acts as a binding agent, holding the rock fragments together. It can consist of minerals like clay, silt, and sand, as well as volcanic ash or other finer particles.
Cement: Over time, as the agglomerate rock undergoes diagenesis (the process of compaction and cementation), minerals can precipitate from pore fluids and bind the clasts together more firmly. This cementation strengthens the rock and contributes to its overall durability.
Formation: Agglomerate rocks typically form in environments where there are energetic processes that transport and deposit large rock fragments. Volcanic settings are one common environment for agglomerate rock formation. During explosive volcanic eruptions, rocks and other materials are violently ejected into the air. These ejected fragments, which can range in size from small ash particles to large boulders, fall back to the ground and accumulate over time. As subsequent eruptions occur, more material can be added to the agglomerate, further cementing the fragments together.
Agglomerate rocks can also form in other settings, such as alluvial fans (fan-shaped sediment deposits formed by flowing water), riverbeds, and areas of active tectonic activity where rocks are broken apart and transported by landslides or other erosional processes.
In summary, agglomerate rock is a type of sedimentary rock composed of coarse clasts bound together by a finer-grained matrix and cement. It forms in environments characterized by energetic processes that transport and deposit large rock fragments, with volcanic settings being a prominent example.
Formation Process of Agglomerate Rock
The formation of agglomerate rock involves a series of geological processes that result in the accumulation, transport, and cementation of coarse rock fragments. The key steps in the formation process are as follows:
Fragmentation: The process begins with the fragmentation of pre-existing rocks. This can occur through various geological mechanisms, such as volcanic eruptions, landslides, rockfalls, or even meteorite impacts. In the case of volcanic eruptions, magma is forcefully expelled from the Earth’s interior and breaks apart into smaller fragments as it reaches the surface.
Transport: The broken rock fragments, or clasts, are transported by agents such as gravity, water (rivers, streams, or ocean currents), ice (glacial movement), or wind. The energy of these transporting agents determines the distance the clasts travel and the manner in which they are sorted based on size.
Deposition: As the transporting agents lose their energy, the clasts settle and are deposited in a particular location. The size of the clasts influences how far they are transported before coming to rest. Larger, heavier clasts tend to settle closer to the source, while smaller, lighter clasts can be transported farther.
Accumulation: Over time, as more clasts are transported and deposited in the same area, an accumulation of these fragments occurs. This accumulation forms a loose pile or layer of clasts, which may have variable sizes, shapes, and degrees of rounding.
Cementation: The final step in agglomerate rock formation involves the process of cementation. As sediment accumulates, mineral-rich fluids percolate through the pores between the clasts. These fluids can deposit minerals that act as cement, binding the clasts together and solidifying the sediment into a coherent rock.
Geological Significance of Agglomerate Rock
Agglomerate rocks hold several geological significance and provide insights into Earth’s history and processes:
Volcanic Activity: Agglomerate rocks are often associated with explosive volcanic eruptions. Studying these rocks can provide valuable information about the types of eruptions that occurred in the past, including their magnitude, intensity, and eruption styles.
Paleoenvironmental Reconstruction: The composition of agglomerate rocks, including the types of clasts and minerals present, can offer clues about the source rocks and the environmental conditions in which the sediment was deposited. This information aids in reconstructing past landscapes, climate, and tectonic settings.
Tectonic Activity: Agglomerate rocks can form in areas of active tectonic processes, such as where landslides are common or during periods of intense faulting and folding. Their presence can help geologists understand the geological history and tectonic evolution of a region.
Sedimentary Processes: Agglomerate rocks illustrate the role of sedimentary processes in shaping Earth’s surface. They showcase how particles are transported, sorted, and deposited in different environments, contributing to our understanding of sedimentary geology.
Natural Hazards: The study of agglomerate rocks and their formation processes can help assess and mitigate natural hazards such as volcanic eruptions, landslides, and tsunamis, which can result from the dynamic geological processes associated with these rocks.
In summary, agglomerate rocks provide valuable insights into past geological events, environmental conditions, and Earth’s dynamic processes. They serve as a record of volcanic activity, tectonic processes, and sedimentary dynamics, contributing to our understanding of Earth’s history and its ongoing geological evolution.
Characteristics of Agglomerate Rock
Agglomerate rocks are distinctive sedimentary rocks characterized by their unique features and properties. These characteristics provide valuable information about the rock’s formation, history, and the processes that shaped it. Here are some key characteristics of agglomerate rock:
Clast Composition: Agglomerates consist of a variety of clasts, which are the individual rock fragments that make up the rock. These clasts can be of different sizes, shapes, and types, ranging from pebbles and cobbles to larger boulders. The composition of these clasts can vary widely, depending on the source rocks and geological context.
Angular or Rounded Clasts: The clasts in agglomerate rocks can exhibit different degrees of angularity or roundness. Angular clasts suggest minimal transport, indicating that the fragments may have been recently broken and deposited close to their source. Rounded clasts, on the other hand, indicate more extensive transport, often by water, which has smoothed and rounded the edges over time.
Matrix Material: Agglomerate rocks are bound together by a matrix, which is a finer-grained material that fills the spaces between the clasts. The matrix can consist of various materials, such as clay, silt, sand, or even volcanic ash. The composition of the matrix provides insights into the sedimentary environment in which the rock formed.
Cementation: Over time, the clasts and matrix in agglomerate rocks can become cemented together by minerals that precipitate from pore fluids. This cementation can range from weak to strong, affecting the overall durability and hardness of the rock.
Texture: The texture of agglomerate rocks can vary from coarse to very coarse, reflecting the larger clasts present. The presence of different-sized clasts creates a heterogeneous texture that distinguishes agglomerate from other sedimentary rocks.
Layering and Bedding: Agglomerate rocks often exhibit layering or bedding, which results from the accumulation of clasts over time. Each layer represents a distinct event of sediment deposition, and the orientation of the layers can provide information about the direction of sediment transport.
Sedimentary Structures: Within agglomerate rocks, sedimentary structures such as cross-bedding, ripple marks, and imbrication (overlapping arrangement of clasts) may be preserved. These structures provide insights into the dynamics of the transporting agents and the depositional environment.
Color: The color of agglomerate rocks can vary based on the types of clasts and matrix materials present. Clasts derived from different source rocks can contribute to a diverse color palette, ranging from dark to light hues.
Fossil Content: While agglomerate rocks are not typically known for preserving fossils, in some cases, fossils may be entrained within the clasts or deposited as part of the matrix. Fossils found in agglomerate rocks can offer insights into the organisms present in the surrounding environment.
Geological Setting: Agglomerate rocks are commonly associated with volcanic environments, especially explosive volcanic eruptions. Their occurrence can provide clues about past volcanic activity, tectonic processes, and landscape evolution.
In summary, agglomerate rocks are characterized by their diverse clast composition, matrix material, cementation, texture, sedimentary structures, and other features. These characteristics collectively provide valuable information about the rock’s origin, depositional environment, and the geological processes that contributed to its formation.
Types and Varieties of Agglomerate Rock
Agglomerate rocks come in various types and varieties, each with distinct characteristics based on their composition, source materials, and depositional environments. Here are some notable types and varieties of agglomerate rock:
Volcanic Agglomerate: This is the most common type of agglomerate and is formed during explosive volcanic eruptions. It consists of a mixture of volcanic fragments, including volcanic rocks, pumice, ash, and other pyroclastic materials. The clasts in volcanic agglomerates can range in size from small pebbles to large boulders and are often angular or rounded, depending on the level of transport.
FaultBreccia: In areas of tectonic activity, such as fault zones, agglomerate-like rocks known as fault breccias can form. These rocks result from the fracturing and fragmentation of rocks along faults, followed by the accumulation of broken fragments in the fault zone.
Megabreccia: Megabreccia refers to a coarse-grained rock made up of exceptionally large clasts, often several meters in diameter. These clasts can be angular or rounded and are typically held together by a matrix. Megabreccias can form in a variety of environments, including volcanic settings, landslides, and impact craters.
Alluvial Fan Agglomerate: Agglomerate rocks can form in alluvial fan environments where sediment is transported and deposited by flowing water. The clasts in these rocks can come from a variety of sources and may include both local and distant materials.
Glacial Tillite: In glacial environments, agglomerate-like rocks known as tillites can form. These rocks are composed of a mixture of rock fragments, clay, and other materials that have been deposited by glaciers. Tillites often exhibit a mixture of angular and rounded clasts.
Submarine Volcanic Agglomerate: Underwater volcanic eruptions can result in the deposition of volcanic fragments in marine or aquatic environments. Submarine volcanic agglomerates may contain volcanic glass fragments and other materials that are indicative of underwater volcanic activity.
Impact Breccia: In impact craters formed by meteorite impacts, impact breccias can be created. These rocks are composed of shattered rock fragments generated by the intense pressure and heat of the impact event. Impact breccias are often found within or around the central region of impact craters.
Fluvial Agglomerate: Agglomerate rocks can also form in riverbeds and fluvial environments where coarse materials are transported and deposited by flowing water. The clasts in fluvial agglomerates are typically well-rounded due to the abrasion that occurs during transport.
Mixed Agglomerates: Some agglomerate rocks may be mixed or composite, containing a combination of different types of clasts and materials from various sources. These mixed agglomerates can provide insights into complex depositional environments and processes.
Exotic Clast Agglomerate: In some cases, agglomerate rocks can contain clasts that are significantly different in composition from the surrounding matrix, indicating long-distance transport or multiple sediment sources.
These are just a few examples of the types and varieties of agglomerate rocks. The specific characteristics and features of each type depend on factors such as the source of clasts, the depositional environment, and the geological processes involved in their formation. Studying these different agglomerate types can provide valuable information about past geological events, volcanic activity, tectonic processes, and sedimentary dynamics.
Conclusion
Agglomerate rocks are distinctive sedimentary formations characterized by their unique composition, texture, and origin. These rocks are primarily composed of coarse clasts held together by a matrix and cementing minerals. They form through various processes, including volcanic eruptions, tectonic activity, and sediment transport, and their characteristics provide valuable insights into Earth’s geological history and processes.
Summary of Agglomerate Rock Characteristics:
Agglomerate rocks exhibit several key characteristics:
Clast Composition: Agglomerates consist of a variety of clasts, ranging from pebbles to boulders, derived from different sources.
Matrix Material: A finer-grained matrix fills the spaces between clasts, comprising materials like clay, silt, sand, or volcanic ash.
Cementation: Minerals precipitate from pore fluids to cement clasts and matrix, enhancing rock strength.
Texture: Agglomerates have a coarse or very coarse texture, reflecting their large clast size.
Angular or Rounded Clasts: Clasts can be angular or rounded, providing insights into transportation distance and energy.
Layering and Bedding: Agglomerates often exhibit layering or bedding, representing distinct depositional events.
Sedimentary Structures: Features like cross-bedding and ripple marks offer clues about sediment transport.
Color: Color varies based on clast and matrix composition.
Geological and Scientific Importance:
Agglomerate rocks hold significant geological and scientific importance:
Volcanic Activity: Agglomerates formed during explosive volcanic eruptions reveal past volcanic events and their intensity.
Tectonic Activity: Agglomerates associated with faults and tectonic processes provide insights into regional geodynamics.
Paleoenvironmental Reconstruction: Agglomerates aid in reconstructing past landscapes, climates, and sedimentary environments.
Sedimentary Processes: These rocks illustrate sediment transport, sorting, and deposition processes.
Natural Hazards: Studying agglomerates contributes to understanding and mitigating volcanic hazards and other geological risks.
Relevance to Earth’s Geological History:
Agglomerate rocks provide a window into Earth’s past:
Volcanic History: Agglomerates offer records of past volcanic activity and eruption styles.
Tectonic Evolution: They reveal information about tectonic processes and landscape changes over time.
Climate Change: Agglomerates can indicate shifts in sediment transport patterns related to changing climates.
Sedimentary Dynamics: By examining agglomerates, scientists gain insights into the interactions of various geological forces.
Environmental Context: Agglomerates provide context for understanding the environments in which they formed.
In conclusion, agglomerate rocks are fascinating geological formations with diverse origins and characteristics. Their composition, formation processes, and scientific significance contribute to our understanding of Earth’s geological history, past landscapes, and the dynamic processes that have shaped our planet over millions of years.
Tuff rock, also simply known as “tuff,” is a type of sedimentary rock that forms from the consolidation of volcanic ash and other volcanic debris. It is a unique rock type that results from explosive volcanic eruptions, during which a mixture of hot ash, rock fragments, and gases is expelled into the atmosphere. As these materials settle and accumulate, they can eventually become compacted and cemented to form tuff rock.
Name origin: The name of Tuff driven from the Italian tufo, also
known as volcanic tuff
Texture: Pyroclastic
Origin: Extrusive/Volcanic
Chemical Composition:
Felsic
Color: Light to
dark brown
Mineral Composition:
Predominantly Glass
Miscellaneous: Light
gray pumice fragments in white ash matrix
Tectonic Environment:
Convergent Boundary – Andean-type subduction zones, intracontinental hot spots
and rifts
Tuff is a type of sedimentary rock formed from the consolidation of volcanic ash and other volcanic debris. It can exhibit a wide range of characteristics based on its mineral composition, texture, and the processes involved in its formation. Tuff classification and composition can be described as follows:
Classification based on Texture:
Lithic Tuff: Lithic tuffs are composed mainly of volcanic rock fragments and ash. They have a fragmental texture and often contain angular to rounded rock fragments of various sizes.
Vitric Tuff: Vitric tuffs are rich in volcanic glass fragments and have a glassy appearance. They may also contain smaller mineral crystals embedded in the glass matrix.
Crystal Tuff: Crystal tuffs have a significant amount of mineral crystals, such as feldspar, quartz, and mica, embedded in a finer matrix of volcanic ash. These crystals can be phenocrysts that originated from the magma before eruption.
Ash-Fall Tuff: Ash-fall tuffs result from the direct settling of fine volcanic ash particles from the atmosphere. They often have a fine-grained texture and can be widespread.
Classification based on Composition:
Rhyolitic Tuff: Rhyolitic tuffs are composed of volcanic ash and debris from rhyolitic eruptions. They typically contain a high proportion of silica-rich minerals, such as quartz and feldspar.
Andesitic Tuff: Andesitic tuffs are derived from andesitic volcanic eruptions and have a composition intermediate between rhyolitic and basaltic tuffs. They may contain minerals like plagioclase feldspar and amphibole.
Basaltic Tuff: Basaltic tuffs originate from basaltic volcanic activity and contain minerals like pyroxene and olivine. They often have a darker color due to the presence of mafic minerals.
Other Characteristics:
Pumiceous Tuff: Pumiceous tuffs are rich in pumice, which is a highly vesicular volcanic glass with a frothy texture. These tuffs are often lightweight and have excellent insulating properties.
Tuffaceous Sandstone: Tuffaceous sandstone is a rock that contains a significant amount of tuff fragments along with sand-sized grains. It represents a transition between tuff and sandstone.
Tuff composition can vary widely depending on the specific volcanic source, eruption style, and subsequent diagenetic processes. Major minerals found in tuff include quartz, feldspar (both plagioclase and potassium feldspar), mica, volcanic glass, and various accessory minerals. The presence of phenocrysts, mineral alteration, and weathering products can further influence the composition of tuff.
In summary, tuff classification and composition are influenced by factors such as volcanic source material, eruption dynamics, deposition conditions, and subsequent geological processes. These variations contribute to the diverse range of tuff types and their importance in understanding Earth’s history and geological processes.
Welded tuff
Welded tuff
Welded tuff is a pyroclastic rock that was sufficiently hot
at the time of deposition to weld together. If the rock contains scattered,
pea-sized fragments or fiamme in it, it is generally called a welded
lapilli-tuff. During welding, the glass shards and pumice fragments stick
together, deform and compact.
Rhyolitic tuff
Rhyolitic tuff
Tuff is generally classified according to nature of the
volcanic rock of which it consists. Rhyolite tuffs contain pumiceus, glassy
fragments and small scoriae with quartz, alkali feldspar, biotite, etc. The
broken pumice is clear and isotropic, and very small particles commonly have
crescentic, sickle-shaped, or biconcave outlines, showing that they are
produced by the shattering of a vesicular glass, sometimes described as
ash-structure.
Trachyte tuffs contain little or no quartz, but much sanidine or anorthoclase and sometimes oligoclase feldspar, with occasional biotite, augite, and hornblende. In weathering, they often change to soft red or yellow clay-stones, rich in kaolin with secondary quartz.
Andesitic tuff
Andesitic tuff
In color, they are red or brown; their scoriae fragments are of all sizes from huge blocks down to minute granular dust. The cavities are filled with many secondary minerals, such as calcite, chlorite, quartz, epidote, or chalcedony; in microscopic sections, though, the nature of the original lava can nearly always be made out from the shapes and properties of the little crystals which occur in the decomposed glassy base.
Basaltic tuff
Basaltic tuff
Basaltic tuffs are also of widespread occurrence both in districts where volcanoes are now active and in lands where eruptions have long since ended. They are black, dark green, or red in colour; vary greatly in coarseness, some being full of round spongy bombs a foot or more in diameter; and being often submarine, may contain shale, sandstone, grit, and other sedimentary material, and are occasionally fossiliferous.
Ultramafic tuff
Ultramafic tuffs are extremely rare; their characteristic is the abundance of olivine or serpentine and the scarcity or absence of feldspar and quartz. Rare occurrences may include unusual surface deposits of maars of kimberlites of the diamond-fields of southern Africa and other regions. The principal rock of kimberlite is a dark bluish-green, serpentine-rich breccia (blue-ground) which when thoroughly oxidized and weathered becomes a friable brown or yellow mass (the “yellow-ground”).
Folding and metamorphism
In course of time, changes other than weathering may overtake tuff deposits. Sometimes, they are involved in folding and become sheared and cleaved. The green color is due to the large development of chlorite. Among the crystalline schists of many regions, green beds or green schists occur, which consist of quartz, hornblende, chlorite or biotite, iron oxides, feldspar, etc., and are probably recrystallized or metamorphosed tuffs. They often accompany masses of epidiorite and hornblende – schists which are the corresponding lavas and sills. Some chlorite-schists also are probably altered beds of volcanic tuff.
Formation Process of Tuff Rock
Volcanic Eruptions and Ash Generation: Tuff rock forms as a result of explosive volcanic eruptions. During such eruptions, molten rock, ash, gas, and other volcanic materials are violently expelled from a volcanic vent. The erupted materials can include fine ash particles, larger rock fragments, pumice, and even molten lava. The explosiveness of the eruption is often influenced by the composition of the magma, with silica-rich magmas tending to produce more explosive eruptions.
Deposition and Compaction of Volcanic Ash: Once ejected into the atmosphere, the volcanic ash and other debris are carried by winds and gravity. Over time, these materials settle back down to the Earth’s surface. The finer ash particles can travel great distances, forming layers of volcanic ash that cover a wide area. As these layers accumulate, they create stratigraphic sequences of ash deposits. The weight of the accumulating layers, combined with further sedimentation and water infiltration, leads to compaction of the volcanic ash.
Diagenesis and Lithification of Tuff: Diagenesis refers to the physical and chemical changes that occur to sediments as they are buried and compacted over time. In the case of tuff, diagenesis plays a crucial role in transforming loose volcanic ash deposits into solid rock. Here are the steps involved:a. Compaction: As layers of volcanic ash accumulate, the weight of overlying sediments compacts the ash particles, reducing the pore spaces between them.b. Cementation: As groundwater percolates through the compacted ash layers, it carries dissolved minerals in solution. These minerals can precipitate and fill the pore spaces between the ash particles, acting as a natural cement that binds the particles together.c. Mineralization: Over time, the minerals within the groundwater may react with the volcanic ash, leading to the formation of new minerals or alteration of existing ones. This mineralization further strengthens the rock.d. Lithification: The combination of compaction, cementation, and mineralization leads to the lithification of the volcanic ash layers, transforming them into solid tuff rock. The once-loose ash becomes a coherent rock unit with defined layers and a consolidated structure.
The resulting tuff rock can exhibit a range of textures, from fine-grained to coarse-grained, depending on factors such as the size of the original volcanic particles, the degree of compaction, and the types of minerals that precipitate during diagenesis. Tuff rock is often characterized by its light color and porous nature, making it distinct from other types of sedimentary rocks. Over time, tuff rock can become an integral part of the geological record, providing insights into past volcanic activity and environmental conditions.
Geological Characteristics of Tuff Rock
Texture, Grain Size, and Porosity:
Texture: Tuff rock can exhibit a variety of textures, depending on factors such as the size of volcanic particles and the degree of compaction. It can range from fine-grained to coarse-grained. Fine-grained tuff has smaller, closely packed particles, while coarse-grained tuff has larger, more loosely arranged particles.
Grain Size: The grain size of tuff is determined by the size of the volcanic ash and debris that make up the rock. This can vary from microscopic particles to visible rock fragments and pumice. Coarse-grained tuff may have distinct layers or bands of different-sized particles.
Porosity: Tuff is typically characterized by its porosity, which refers to the amount of open space or voids within the rock. The porosity of tuff is a result of the original spaces between volcanic particles and the subsequent compaction and cementation processes. High porosity can impact the rock’s strength, water-holding capacity, and other physical properties.
Mineral Composition and Presence of Phenocrysts:
Mineral Composition: The mineral composition of tuff is primarily determined by the minerals present in the original volcanic ash and debris. Common minerals found in tuff include quartz, feldspar, mica, and various volcanic glass fragments. These minerals may undergo alteration and mineralization during diagenesis, leading to the formation of new minerals.
Phenocrysts: Phenocrysts are larger crystals that can be embedded within the fine-grained matrix of tuff. These crystals are often formed within the volcanic magma before eruption and are then incorporated into the ash and debris during the eruption. The presence of phenocrysts can provide clues about the composition and origin of the volcanic material.
Color Variations and Geological Implications:
Color: Tuff rock can display a wide range of colors, including shades of white, gray, brown, red, and even green, depending on the mineral content and the presence of iron oxide and other pigments. The coloration can be influenced by the original composition of the volcanic material, as well as subsequent chemical changes and weathering processes.
Geological Implications: Color variations in tuff can provide valuable information about the depositional environment, the volcanic source, and the history of the rock. For example:
Light-colored tuff may indicate a higher proportion of silica-rich volcanic material.
Darker colors might suggest the presence of volcanic glass or mafic minerals.
Red or brown hues often result from the presence of iron oxides, which can indicate oxidizing conditions.
Greenish tuffs may be associated with volcanic activity rich in magnesium and iron.
Color changes within layers can reflect changes in volcanic activity over time.
Geologists use these geological characteristics, along with other field observations and laboratory analyses, to interpret the origin, depositional history, and potential environmental conditions during the formation of tuff rock. Studying tuff can provide insights into past volcanic eruptions, sedimentary processes, and changes in Earth’s surface through geologic time.
Distribution and Occurrence of Tuff Rock
Global Distribution of Tuff Deposits: Tuff deposits are found in various parts of the world, often associated with regions of past or present volcanic activity. They can be located near active volcanoes, along volcanic arcs, within volcanic calderas, or in areas where ancient volcanic activity occurred. Tuff deposits are present on nearly every continent and can provide valuable insights into the history of volcanic activity and the geologic evolution of different regions.
Tuff Rock Formations in Specific Volcanic Regions:
Mediterranean Region: The Mediterranean region is well-known for its tuff formations. The city of Rome, for instance, is built upon tuff deposits, and many historical sites, such as the Colosseum and the Roman Forum, feature tuff-based structures.
Yellowstone National Park, USA: The Yellowstone Caldera, a supervolcano, has produced massive tuff deposits over its history. The park is home to the famous Yellowstone tuff, a series of volcanic ash deposits resulting from past eruptions.
Cappadocia, Turkey: This region is famous for its unique tuff formations known as “fairy chimneys.” Tuff erosion has created stunning rock formations that have been used as dwellings, churches, and other structures.
Tuff Rings and Cones: Some volcanic regions, such as New Zealand and parts of the United States, feature tuff rings and cones formed by explosive phreatomagmatic eruptions. These eruptions involve the interaction of magma with water, resulting in the ejection of steam and ash.
Significance of Tuff Rock in Understanding Past Volcanic Activity:
Eruption History: Tuff deposits provide a record of past volcanic eruptions, including information about eruption frequency, intensity, and style. Studying the layers and characteristics of tuff can help scientists reconstruct the history of volcanic activity in a region.
Volcanic Hazards: Analyzing tuff formations can help assess the potential hazards posed by volcanoes. By understanding the types of eruptions that produced tuff deposits, scientists can better predict and prepare for future volcanic events.
Depositional Processes: Tuff deposits offer insights into the processes of ash deposition, sedimentation, and erosion. They can help researchers understand how volcanic materials are transported by air and water, contributing to the overall understanding of sedimentary processes.
Climate and Environmental Changes: The mineral composition and geochemical characteristics of tuff can provide information about the environmental conditions at the time of eruption. Tuff layers can serve as markers for specific geological time periods and can aid in studying past climate changes.
Magmatic Evolution: The mineralogy and chemistry of tuff can reveal details about the composition and evolution of the magma source. Phenocrysts and mineral assemblages within tuff can offer insights into the nature of the volcanic plumbing system.
Dating Techniques: Tuff deposits often contain minerals that can be dated using radiometric dating methods. These dates help establish a chronological framework for volcanic and geological events, aiding in the construction of geological timelines.
In summary, tuff rock deposits are valuable geological archives that provide information about past volcanic activity, depositional processes, and environmental conditions. They contribute to our understanding of Earth’s history, the dynamics of volcanic systems, and the interactions between the geosphere and the surrounding environment.
Petrological Analysis of Tuff Rock
Petrological analysis involves the detailed study of rocks, including tuff, at a microscopic and macroscopic level to understand their mineralogical composition, texture, and overall origin. Here’s how the process of petrological analysis for tuff samples typically unfolds:
Sample Preparation:
Tuff samples are collected from field locations or drill cores.
Samples are cut into thin sections using specialized equipment, resulting in thin slices of rock that can be studied under a petrographic microscope.
Microscopic Examination:
Thin sections of tuff are observed under a petrographic microscope, which allows for detailed examination of mineral composition, texture, and relationships between mineral grains.
Key features, such as mineral shapes, sizes, colors, and orientations, are noted.
Identification of Minerals and Components:
Mineral identification involves using various optical properties, such as birefringence, color, and cleavage, to determine the minerals present.
Common minerals found in tuff include quartz, feldspar, mica, volcanic glass, and various accessory minerals.
Phenocrysts, if present, are identified and their mineralogy noted. Phenocrysts are larger crystals embedded within the finer matrix of the tuff.
Texture and Structures:
Petrologists examine the texture of the tuff, which includes characteristics like grain size, grain arrangement, and presence of vesicles (gas bubbles).
Vesicles can provide insights into the degree of explosiveness of the eruption and the gas content of the magma.
Geochemical Analysis and Insights into Volcanic History:
Geochemical analysis involves determining the chemical composition of the tuff, including major and trace elements.
X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) are common techniques for geochemical analysis.
Geochemical data can provide insights into the source of the volcanic material, the nature of the magma, and potential changes in volcanic activity over time.
Isotopic analyses (e.g., radiogenic isotopes) can help determine the age of the tuff and the underlying volcanic processes.
Mineral Alteration and Weathering:
Petrologists assess any signs of mineral alteration or weathering, which can provide information about post-depositional changes in the tuff.
Integration of Results:
The results from microscopic examination, mineral identification, texture analysis, and geochemical studies are integrated to build a comprehensive understanding of the tuff’s petrological characteristics and its geologic history.
Petrological analysis of tuff samples is crucial for unraveling the story of past volcanic events, understanding the conditions under which tuff deposits formed, and deciphering the broader geological context of a region. This analysis contributes to our knowledge of volcanic processes, magmatic evolution, and Earth’s dynamic history.
Engineering and Industrial Applications of Tuff Rock
Use of Tuff Rock as Construction Material: Tuff rock has been used as a construction material for centuries due to its favorable properties, such as its lightweight nature, ease of quarrying, and workability. Some of its applications in construction include:
Building Facades: Tuff can be cut into blocks or carved to create decorative facades and architectural details for buildings.
Structural Components: Tuff blocks can be used as load-bearing walls and structural elements in construction projects.
Ornamental Elements: Tuff’s softness allows for intricate carving, making it suitable for ornamental features, sculptures, and reliefs.
Historical and Cultural Heritage: Many ancient structures and monuments around the world are constructed from tuff, contributing to their historical and cultural significance.
Tuff as a Lightweight Aggregate in Concrete: Tuff can also be crushed and used as a lightweight aggregate in concrete production. Lightweight concrete made with tuff aggregates offers several advantages:
Reduced Weight: Lightweight concrete made with tuff aggregates is significantly lighter than traditional concrete, making it useful in applications where weight is a concern.
Thermal Insulation: The porous nature of tuff can contribute to improved thermal insulation properties in lightweight concrete.
Reduced Shrinkage: Tuff aggregates can help reduce the overall shrinkage of concrete, leading to improved durability.
Workability: Lightweight concrete made with tuff aggregates can have improved workability, making it easier to place and finish.
Tuff’s Role in Geothermal Energy Production: Tuff rock has a significant role in geothermal energy production, particularly in areas with high-temperature geothermal resources. Geothermal power plants harness the heat from Earth’s interior to generate electricity. Tuff’s properties contribute to this process:
Reservoir Rock: Tuff can act as a reservoir rock that contains hot water or steam generated by subsurface heat. The porous nature of tuff allows for the storage and movement of geothermal fluids.
Permeability: Tuff’s permeability allows geothermal fluids to flow through fractures and pores, facilitating the circulation of hot fluids that can be used to generate energy.
Enhanced Geothermal Systems (EGS): Tuff formations can also be used in enhanced geothermal systems, where water is injected into hot rocks to create artificial geothermal reservoirs for energy production.
Tuff’s versatility, lightweight nature, and porous properties make it suitable for a range of engineering and industrial applications. Its use in construction, concrete production, and geothermal energy underscores its importance in contributing to sustainable development and resource utilization.
Archaeological and Paleontological Significance of Tuff Rock
Tuff as a Preservation Medium for Fossils: Tuff rock can play a crucial role in the preservation of fossils due to its rapid burial and protective properties. When volcanic ash and debris cover organisms and other materials, they create a protective environment that can prevent or delay decay. This process, known as taphonomy, can lead to exceptional fossil preservation, capturing details that might otherwise be lost. Fossils preserved within tuff deposits provide valuable insights into ancient ecosystems, species, and evolutionary history.
Role of Tuff in Archaeological Dating and Stratigraphy: Tuff deposits are important markers in archaeological and geological stratigraphy. They can be used for dating and correlating different layers of sedimentary and volcanic rocks:
Radiometric Dating: Some minerals within tuff deposits, such as zircon or feldspar, contain radioactive isotopes that decay over time. By analyzing the ratios of parent and daughter isotopes, scientists can determine the age of the tuff layer, providing a minimum age for the fossils or artifacts found within it.
Relative Dating: Tuff layers act as temporal markers, allowing archaeologists and geologists to establish the relative sequence of events in different locations. Tuff layers can be correlated across sites based on their unique mineralogy and composition.
Famous Tuff Sites and Their Historical Importance:
Laetoli, Tanzania: Tuff layers at the Laetoli site contain footprints of early hominins, providing valuable information about their behavior and locomotion nearly 3.6 million years ago.
Pompeii and Herculaneum, Italy: The eruption of Mount Vesuvius in 79 AD covered the ancient Roman cities of Pompeii and Herculaneum in tuff and volcanic ash. This preserved these cities, including buildings, artwork, and even the remains of inhabitants, offering a unique snapshot of Roman life at the time.
Olduvai Gorge, Tanzania: Tuff layers at Olduvai Gorge have yielded important archaeological and paleontological finds, including stone tools and hominin remains, contributing to our understanding of human evolution.
Taung, South Africa: Tuff layers at Taung contained the fossilized skull of the “Taung Child,” an early hominin of the species Australopithecus africanus, discovered by Raymond Dart in 1924.
These tuff sites and many others have provided crucial insights into human history, evolution, and the ancient environments in which our ancestors lived. Tuff’s role in preserving fossils and establishing chronological frameworks has contributed significantly to our understanding of Earth’s past and the development of life on our planet.
Scoria is a type of volcanic rock that forms from the solidification of molten lava. It is commonly found around and on the surface of active and dormant volcanoes. Scoria has distinctive characteristics that make it unique and recognizable among other types of volcanic rocks.
Definition: Scoria is an extrusive igneous rock, meaning it is formed from lava that has erupted from a volcano and cooled quickly on the Earth’s surface. It is often referred to as “lava rock” due to its origin from lava flows. Scoria is composed primarily of vesicles (small cavities) and solidified lava fragments. These vesicles are the result of gas bubbles escaping from the molten lava during its rapid cooling and solidification.
Name Origin: The
word scoria comes from the Greek “skoria”= rust
Texture:
aphanitic and vesicular (contains abundant large gas cavities)
Composition:
intermediate (andesitic) to mafic (basaltic)
Other Characteristics:
vesicular like pumice, but denser and darker with larger vesicles
Origin: Extrusive/Volcanic
Mineral Composition:
Predominantly Glass
Tectonic Environment: Divergent Boundary or Intra-oceanic hot
spots
Comparisons: Scoria differs from pumice, another vesicular volcanic rock, in having larger vesicles and thicker vesicle walls, and hence is denser. The difference is probably the result of lower magma viscosity, allowing rapid volatile diffusion, bubble growth, coalescence, and bursting.
Formation and Composition: Scoria forms as a result of volcanic activity and the solidification of molten lava. When magma (molten rock beneath the Earth’s surface) reaches the surface during a volcanic eruption, it is called lava. This lava often contains dissolved gases, such as water vapor and carbon dioxide. As the lava reaches the lower pressure of the Earth’s surface, these gases start to come out of solution and form bubbles within the lava.
The rapid cooling of the lava on the surface causes the bubbles to become trapped within the solidifying rock. This leads to the characteristic vesicles (cavities) that are a defining feature of scoria. The vesicles can vary in size and distribution, giving different scoria samples their unique appearances.
The composition of scoria is primarily determined by the composition of the magma from which it forms. Generally, scoria is rich in iron and magnesium, which gives it its dark color. It also contains other minerals that are common in volcanic rocks, such as feldspar and pyroxene. The specific mineral composition can vary widely based on the source magma and local geological conditions.
Geological Occurrence: Scoria is commonly found in regions with recent or past volcanic activity. It is often associated with basaltic or andesitic volcanic eruptions. Some of the key geological occurrences of scoria include:
Volcanic Cones and Craters: Scoria is often found around the vent of a volcano and within its craters. During eruptions, scoria may accumulate in the immediate vicinity of the vent, forming cone-shaped hills or mounds known as volcanic cones.
Lava Flows: Scoria is frequently observed on the surface of lava flows, where it can accumulate in layers. As the lava flows down the sides of a volcano and cools, scoria can solidify and form a rough and porous surface.
Tephra Deposits: Tephra refers to any fragmented material that is ejected during a volcanic eruption, including ash, lapilli (small rock fragments), and scoria. Scoria can be found in tephra deposits that have settled over a wider area around a volcano.
Cinder Cones: Cinder cones are small, steep-sided volcanoes that are often built up from the accumulation of volcanic ash, lapilli, and scoria ejected during relatively mild eruptions.
Volcanic Plateaus: In some cases, large lava plateaus or flows can form extensive layers of scoria. These plateaus are the result of massive lava eruptions that cover large areas with thick layers of lava and scoria.
Historical and Recent Eruptions: Scoria can also be found in regions with historical or recent volcanic eruptions. In areas with ongoing volcanic activity, such as the Pacific Ring of Fire, scoria can continue to accumulate on the surface over time.
Overall, scoria’s geological occurrence is closely tied to volcanic processes and can provide valuable insights into a region’s volcanic history and activity.
Scoria, a type of volcanic rock, possesses distinct physical properties that stem from its unique formation process and composition. Here are some of the key physical properties of scoria:
Texture: Scoria typically has a porous and vesicular texture, which means it contains numerous cavities or vesicles formed by trapped gas bubbles during the rapid cooling and solidification of lava. The vesicles give scoria a rough, sponge-like appearance.
Color: Scoria comes in a range of colors, including black, reddish-brown, dark brown, and variations in between. The color is often influenced by the presence of minerals such as iron and magnesium.
Density: Due to its high porosity, scoria is relatively lightweight compared to other rocks. Its density can vary, but it is generally less dense than denser volcanic rocks like basalt. This characteristic makes scoria useful for various applications, such as lightweight aggregates.
Porosity: Scoria is characterized by its high porosity, which is a measure of the amount of open space (pores, voids, or vesicles) within the rock. The vesicles are irregularly shaped and can vary in size, contributing to the overall porous nature of the rock.
Hardness: Scoria is not as hard as some other volcanic rocks like basalt. It can be relatively easy to break apart or crush, making it suitable for certain construction and decorative uses.
Weight: As a lightweight rock, scoria is often used in applications where weight is a concern, such as in the production of lightweight concrete, garden landscaping, and as an aggregate in lightweight cinder blocks.
Luster: Scoria typically has a dull to matte luster, which means it does not exhibit a reflective or shiny appearance when light is shone upon it.
Fracture: Scoria generally exhibits a rough and irregular fracture pattern, consistent with its porous and vesicular nature.
Heat Insulation: The porous structure of scoria makes it a good insulator of heat and sound. This property has led to its use in some construction and insulation applications.
Water Absorption: Scoria’s porosity allows it to absorb and retain water, which can be advantageous in certain gardening and horticultural applications.
Weathering: Over time, scoria can undergo weathering and erosion due to exposure to the elements, causing the rock to break down and the vesicles to become more rounded.
Specific Uses: Because of its physical properties, scoria has been used in a variety of ways, including as a lightweight aggregate in concrete, for decorative landscaping purposes, and in the production of lightweight construction materials.
It’s important to note that the specific physical properties of scoria can vary depending on factors such as its mineral composition, cooling rate, and geological environment.
Uses of Scoria
Uses of Scoria
Scoria, with its unique properties, has been utilized for various practical and decorative purposes. Its lightweight and porous nature make it suitable for specific applications. Here are some common uses of scoria:
Construction Aggregates: Scoria can be crushed and used as an aggregate material in construction projects such as concrete and asphalt. Its lightweight nature helps reduce the overall weight of the construction material, which can be advantageous in certain applications.
Lightweight Concrete: Scoria aggregates are often used in the production of lightweight concrete. This type of concrete is suitable for situations where a reduced overall weight is desired, such as in the construction of buildings, bridges, and other structures.
Cinder Blocks: Scoria can be incorporated into the production of lightweight cinder blocks, which are used in construction for their insulation properties and lower weight compared to traditional concrete blocks.
Drainage and Filtration: The porous nature of scoria makes it useful for drainage and filtration applications. It can be used as a drainage layer in landscaping projects, including garden beds, to promote proper water drainage and prevent waterlogging.
Landscaping and Gardening: Scoria is commonly used in landscaping for pathways, decorative mulching, and rock gardens. Its distinct appearance and texture can add visual interest to outdoor spaces.
Heat and Sound Insulation: Scoria’s porous structure makes it a good insulator of both heat and sound. It has been used in the construction of walls and barriers to help manage temperature and noise.
Horticulture: In gardening, scoria can be used as a growing medium in hydroponic systems or as a component of soil mixes for potted plants. Its water-retention properties can help maintain proper moisture levels for plant growth.
Road and Rail Embankments: Scoria has been used in the construction of road and rail embankments due to its lightweight nature and good drainage properties.
Erosion Control: Scoria can be used to stabilize slopes and prevent erosion in certain landscapes.
Art and Decorative Purposes: Scoria’s unique texture and color make it suitable for artistic and decorative applications, such as sculpture, mosaics, and architectural embellishments.
Geological and Educational Displays: Scoria samples are often used in geological displays and educational settings to showcase volcanic processes and rock types.
Lava Rock Jewelry: Polished and shaped scoria pieces can be used to create jewelry and ornaments.
It’s important to note that while scoria has various practical uses, its lightweight and porous nature may limit its suitability for certain high-strength and load-bearing applications. Additionally, its usage can vary based on regional availability and specific project requirements.
Volcanic Processes and Scoria Formation
Scoria formation is closely tied to volcanic processes and the behavior of magma during volcanic eruptions. Understanding the volcanic processes involved in scoria formation can provide insights into how this unique volcanic rock is created. Here’s an overview of the key volcanic processes that lead to scoria formation:
Magma Generation and Ascent: Volcanic activity begins deep within the Earth’s mantle, where molten rock, known as magma, is generated. This magma is less dense than the surrounding rock, allowing it to rise toward the surface. As magma ascends, it can collect in chambers beneath a volcano.
Gas Dissolution: Magma often contains dissolved gases, including water vapor, carbon dioxide, sulfur dioxide, and others. These gases are under high pressure within the magma due to the depth and confinement of the magma chamber.
Eruption Initiation: When pressure within the magma chamber becomes too great, it can overcome the confining rock and trigger a volcanic eruption. As magma rises, it encounters decreasing pressure, causing the dissolved gases to come out of solution and form bubbles or gas pockets.
Eruption and Lava Flow: During an eruption, magma is expelled from the volcano’s vent. If the magma is relatively viscous (thick and sticky), gas bubbles have difficulty escaping. This can result in a buildup of pressure and explosive eruptions. If the magma is less viscous, it can flow more easily and lead to effusive eruptions with relatively gentle lava flows.
Rapid Cooling and Solidification: As the magma is expelled from the vent and comes into contact with the cooler ambient air or water, it cools rapidly and solidifies. This rapid cooling prevents the gas bubbles from escaping completely, and they become trapped within the solidifying lava.
Formation of Vesicles: The trapped gas bubbles, or vesicles, create voids or cavities within the solid rock. These vesicles give scoria its characteristic porous texture. The size and distribution of the vesicles can vary based on factors such as the magma’s gas content and cooling rate.
Accumulation and Fragmentation: As scoria-rich lava is erupted and flows on the surface, it can accumulate in various ways, forming features like volcanic cones, cinder cones, and lava plateaus. In some cases, the lava can fragment into small pieces, known as lapilli, which contribute to the scoria accumulation.
Cooling and Weathering: Over time, scoria continues to cool and may undergo weathering processes, which can round the edges of vesicles and alter its appearance.
It’s important to note that scoria formation can vary based on the specific characteristics of the magma, the style of volcanic eruption, and the geological environment. Different types of volcanic eruptions, such as explosive eruptions or effusive eruptions, can produce scoria with distinct textures and vesicle distributions. Studying scoria can provide valuable insights into the conditions and processes that occur within volcanic systems.
Comparison with Other Volcanic Rocks
To better understand scoria, it’s helpful to compare it with other types of volcanic rocks. Here’s a comparison between scoria, basalt, and pumice, three common volcanic rocks:
Scoria:
Formation: Forms from rapidly cooled and solidified lava with trapped gas bubbles, creating vesicles.
Texture: Porous and vesicular texture due to vesicle formation. Rough and sponge-like appearance.
Color: Can vary but often black, reddish-brown, or dark brown.
Density: Relatively lightweight due to high porosity.
Uses: Used in construction as lightweight aggregate, in lightweight concrete, cinder blocks, landscaping, and decorative applications.
Basalt:
Formation: Forms from slower cooling of lava on the Earth’s surface or underwater.
Texture: Aphanitic (fine-grained) to porphyritic (larger crystals embedded in fine matrix) texture. May have vesicles but generally fewer than scoria.
Color: Dark gray to black.
Density: Denser than scoria, less porous.
Uses: Used in construction, road building, and as a dimension stone. Also found in natural formations like columns or pillars.
Pumice:
Formation: Forms from highly frothy lava with abundant gas bubbles, leading to rapid vesicle formation.
Texture: Extremely porous and vesicular, often with a frothy appearance. Lightweight and can float in water.
Color: Light gray to white.
Density: Highly porous and very lightweight due to extensive vesicles.
Uses: Used as a lightweight abrasive material, in horticulture (as a soil amendment), and for making lightweight concrete and cinder blocks.
Comparing these volcanic rocks highlights their differences in terms of formation, texture, color, density, and uses. Scoria is distinct for its highly vesicular texture and is valued for its lightweight properties in construction and landscaping. Basalt is known for its fine-grained texture and wide range of applications, while pumice is unique in its extreme porosity and use in abrasive and horticultural applications. Understanding these differences helps geologists and scientists classify and study volcanic rocks and their origins.
Distribution of Scoria
Scoria is found in various volcanic regions around the world, often associated with both active and dormant volcanoes. It is commonly found in areas with recent or historical volcanic activity. Here are some notable volcanic regions and specific volcanoes where scoria deposits can be found:
1. Pacific Ring of Fire: The Pacific Ring of Fire is a horseshoe-shaped zone that encircles the Pacific Ocean and is known for its high levels of volcanic and seismic activity. Many of the world’s most well-known and active volcanoes are located in this region, including those with significant scoria deposits.
Mount St. Helens, USA: The 1980 eruption of Mount St. Helens produced vast amounts of scoria. The eruption caused the north face of the mountain to collapse, resulting in the largest landslide in recorded history.
Sakurajima, Japan: This stratovolcano frequently produces scoria during explosive eruptions. Its ash clouds and volcanic activity have been a recurring feature of the region.
2. East African Rift Valley: This geological rift system in East Africa is known for its active volcanic activity, which has resulted in the formation of various volcanoes and scoria deposits.
Mount Nyiragongo, Democratic Republic of Congo: The volcano’s lava lake is a source of continuous volcanic activity, leading to the formation of scoria deposits.
3. Central Andes, South America: The Andes Mountains are home to many volcanoes and volcanic features, including those that produce scoria.
Villarrica, Chile: Villarrica is one of Chile’s most active volcanoes and has erupted scoria in its explosive eruptions.
4. Italian Volcanoes:Italy has several active volcanoes, including Mount Vesuvius and Stromboli, known for their eruptions and scoria deposits.
Stromboli, Italy: Stromboli is famous for its nearly continuous volcanic activity, producing frequent small eruptions and scoria deposits.
5. Iceland: Iceland’s volcanic activity is linked to its location on the Mid-Atlantic Ridge, a divergent tectonic boundary.
Eyjafjallajökull: The 2010 eruption of Eyjafjallajökull produced scoria and disrupted air travel across Europe due to ash clouds.
These examples showcase the global distribution of scoria and its association with various volcanic regions. Scoria deposits are not limited to these regions, as they can be found in many other areas with volcanic activity. The specific characteristics of scoria and its distribution vary based on the local geological conditions, eruption styles, and other factors.
Geological Significance
Geological Significance of Scoria
Scoria holds significant geological importance as it provides valuable insights into volcanic processes, Earth’s internal dynamics, and the history of volcanic activity. Its study contributes to our understanding of various geological phenomena and processes. Here are some key aspects of the geological significance of scoria:
Volcanic Activity and Eruptions: Scoria is a direct product of volcanic eruptions. Studying scoria deposits and their characteristics can help scientists reconstruct past volcanic events, understand eruption mechanisms, and predict potential future volcanic activity.
Magma Properties: The formation of scoria is influenced by the properties of magma, including its composition, gas content, and viscosity. Analyzing scoria can provide information about the source magma and its behavior during eruption.
Volcanic Hazards: The presence of scoria can indicate areas prone to volcanic hazards. Studying scoria deposits helps identify regions that have experienced volcanic eruptions in the past and can assist in assessing potential risks to human settlements and infrastructure.
Evolution of Volcanic Systems: Scoria deposits from different eruptions can reveal the evolving nature of a volcanic system over time. The size, composition, and distribution of scoria can provide insights into the history of magma chambers, eruption styles, and changes in volcanic activity.
Formation of Cones and Craters: Scoria is a key component in the formation of volcanic cones, cinder cones, and craters. Studying the accumulation and distribution of scoria around these features helps geologists understand the building processes of volcanoes.
Volcanic Geomorphology: Scoria deposits contribute to the overall geomorphology of volcanic landscapes. They can create unique landforms, such as lava plateaus, volcanic cones, and lava flows, which shape the surface of the Earth.
Magma Degassing: The vesicles in scoria provide insights into the degassing process of magma during eruption. The size, shape, and distribution of vesicles can reveal the rate of gas escape from magma and the conditions under which it occurred.
Paleoenvironmental Reconstructions: Scoria deposits can sometimes be found interbedded with other sedimentary rocks. These deposits can be used to reconstruct past environmental conditions and changes, providing information about ancient climates and ecosystems.
Geological Dating: Scoria deposits can be dated using various radiometric dating techniques, helping establish the timing of volcanic events and contributing to the development of geological timelines.
Education and Outreach: Scoria is a visually distinctive rock that is often used in educational displays and public outreach programs to help explain volcanic processes and geological concepts to the general public.
In summary, scoria is more than just a volcanic rock; it is a window into Earth’s dynamic geological history, offering valuable information about volcanic activity, magma behavior, and the shaping of landscapes over time. Its study contributes to our broader understanding of Earth’s geological processes and the interactions between the planet’s surface and its internal processes.
Summary of Scoria’s Importance and Utility
Scoria’s Importance and Utility
Scoria is a volcanic rock with distinctive characteristics that hold both practical and scientific significance. Its unique properties and formation processes contribute to its importance and utility in various fields:
Geological Understanding: Scoria provides valuable insights into volcanic processes, eruption dynamics, and Earth’s internal activity. Its study helps geologists reconstruct past volcanic events, predict potential future eruptions, and understand the behavior of magma.
Volcanic Hazard Assessment: The presence of scoria deposits can indicate areas prone to volcanic activity and hazards. Studying scoria aids in assessing risks to human settlements and infrastructure, contributing to better volcanic hazard management.
Environmental Reconstruction: Scoria deposits offer information about past climates and ecosystems when interbedded with other sediments. They help scientists reconstruct ancient environmental conditions and changes over time.
Educational Outreach: Scoria’s unique appearance makes it an effective tool for educational displays and public outreach. It helps explain volcanic processes, geological concepts, and Earth’s dynamic nature to a broader audience.
Volcanic Landform Formation: Scoria is a fundamental component in the formation of volcanic cones, craters, and other volcanic landforms. Its accumulation contributes to the shaping of landscapes and the development of distinct geological features.
Construction Materials: Scoria’s lightweight and porous nature make it suitable for various construction applications. It is used as an aggregate in lightweight concrete, cinder blocks, and road embankments, reducing overall weight and cost.
Landscaping and Horticulture: Scoria’s use in landscaping adds visual interest to outdoor spaces. Its water-retaining properties make it beneficial for drainage and water management in gardens, while also serving as a decorative element.
Heat and Sound Insulation: The porosity of scoria lends itself to insulation applications, such as in construction materials and sound barriers, contributing to energy efficiency and noise reduction.
Art and Aesthetics: Scoria’s texture and color make it suitable for artistic and decorative purposes, including sculptures, mosaics, and architectural embellishments.
Scientific Research: The study of scoria aids in advancing our understanding of magma behavior, volcanic systems, and Earth’s geological history. Its analysis contributes to the broader field of geology and earth sciences.
In essence, scoria’s importance and utility extend beyond its appearance as a volcanic rock. It serves as a valuable tool for scientific research, a practical resource in construction and landscaping, and a means to educate and engage the public in the wonders of Earth’s geological processes.
Pumice is a volcanic rock that consists of highly vesicular rough textural rock glass. It generally light colored. It is created when gas-saturated liquid magma erupts like a carbonated drink and cools so rapidly that the resulting foam solidifies into a glass full of gas bubbles. Pumices from silica-rich lavas are white, those from lavas with intermediate silica content are often yellow or brown, and rarer silica-poor that are black. The hollows in the froth can be rounded, elongated, or tubular, depending on the flow of the solidifying lava. The glassy material that forms it can be in threads, fibers, or thin partitions between the hollows. Although pumice is mainly composed of glass, small crystals of various minerals occur. Pumice has a low density due to its numerous air-filled pores. For this reason, it can easily float in water
Name origin: The names derived from the Latin word “pumex” which means foam and through history has been given many names because its formation was unclear.
Texture: Aphanitic
and vesicular (contains abundant small gas cavities)
Pumice is primarily Silicon Dioxide, some Aluminum Oxide and trace amounts pf other oxide. Mall crystals of various minerals occur in many pumices; the most common are feldspar, augite, hornblende, and zircon. The cavities (vesicles) of pumice are sometimes rounded and may also be elongated or tubular, depending on the flow of the solidifying lava. The occurring among old volcanic rocks, the cavities are usually filled with deposits of secondary minerals introduced by percolating water. The glass itself forms threads, fibres, and thin partitions between the vesicles. Rhyolite and trachyte pumices are white, andesite pumices often yellow or brown, and pumiceous basalts (such as occur in the Hawaiian Islands) pitch black.
It forms so quickly that its atoms often don’t have time to organize into crystals. Sometimes there are crystals present in pumice, but most of the structure is amorphous, producing a volcanic glass called a mineraloid.
Pumice Formation
The pumice is formed by contact with the lava water. This
occurs most commonly near water or underwater volcanoes. When the hot magma
comes into contact with water, rapid cooling and rapid pressure loss reduce
bubble by forming lava. The cooling of the rock below the melting point of the
rock means that the bubbles are trapped inside when the rock changes into a
solid immediately after contact with water. Since the pumice is irreversible,
it is sometimes like glass and the bubbles are held between the thin
translucent bubble walls of the rock.
Volcanic Gases and Density
If volcanic gases coming from the lava before it cools rapidly, that process can be created to scoria and pumice It is light colored, has a porosity of about 90 percent and is less dense; scoria is more dense with larger bubbles and thicker bubble walls and is quickly dipped in contrast to the floating boom. If there is too much gas, pumice is formed; When less gas is associated with less viscous magma, the scoria is formed. During the volcanic activity near Tonga, pumice swings from underwater volcanic eruptions were produced, and the pumice can be created quickly and in the past.
Shipping around the World
The actual shipping method depends on the end user. For
example, a dentist buys his pumice in a small 2-ounce jar. A manufacturer of
hand soap or a computer circuit board manufacturer will receive pumice
shipments as shrink-wrapped pallets of 44 lb. bags (20 KG) that arrive via
truck or ocean-going container. A public works department using pumice for
water filtration may take delivery of their pumice in bulk rail cars. A
concrete batch plant will accept a load of pumice (used as a natural pozzolan)
in a pneumatic truck. The bottom line is that a company with a pumice deposit
in demand world-wide, such as Hess Pumice, necessarily develops the expertise
and ability to package pumice however the customer needs it packaged and to
ship that pumice efficiently where it’s needed, anywhere in the world.
Where is it located
They are most abundant and most typically developed from felsic (silica-rich) igneous rocks; accordingly, they commonly accompany obsidian. It can be found all around the globe deriving from continental volcanic occurrence and submarine volcanic occurrence. Floating stones can also be distributed by ocean currents.As described earlier it is produced by the eruption of explosive volcanoes under certain conditions, therefore, natural sources occur in volcanically active regions. It is mined and transported from these regions. In 2011, Italy and Turkey led pumice mining production at 4 and 3 million tonnes respectively; other large producers at or exceeding a million tonnes were Greece, Iran, Chile and Syria.
Asia
There are large reserves of pumice in Asian countries
including Afghanistan, Indonesia, Japan, Syria, Iran and eastern Russia.
Considerable amounts of pumice can be found at the Kamchatka Peninsula on the
eastern flank of Russia. This area contains 19 active volcanoes and it lies in
close proximity with the Pacific volcanic belt.
Europe
Europe is the largest producer of pumice with deposits in
Italy, Turkey, Greece, Hungary and Iceland. Italy is the largest producer of
pumice because of its numerous eruptive volcanoes. On the Aeolian Islands of
Italy, the island of Lipari is entirely made up of volcanic rock, including
pumice.
North America
It can be found all across North America including on the Caribbean Islands. In the United States, This rock is mined in Nevada, Oregon, Idaho, Arizona, California, New Mexico and Kansas. U.S. production of pumice and pumicite in 2011 was estimated at 380,000 tonnes, valued at $7.7 million with approximately 46% coming from Nevada and Oregon. Idaho is also known as a large producer of pumice because of the quality and brightness of the rock found in local reserves.
South America
Chile is one of the leading producers of Pumice in the
world.[The Puyehue-Cordón Caulle are two coalesced volcanoes in the Andes
mountains that ejected ash and pumice across Chile and Argentina. A recent
eruption in 2011 wreaked havoc on the region by covering all surfaces and lakes
in ash and pumice.
Africa
Kenya, Ethiopia and Tanzania have some deposits of pumice.
Australia
The Havre Seamount volcano produced the largest-known deep ocean volcanic eruption on Earth. The volcano erupted in July 2012 but remained unnoticed until enormous pieces of pumice were seen to be floating on the Pacific Ocean. Blankets of rock reached a thickness of 5 meters. Most of this floating rock is deposited on the North-West coast of New Zealand and the Polynesia islands action in 2011 was estimated at 17 million tones.
Characteristics and Properties
Pumice is composed of highly microvesicular glass pyroclastic with very thin, translucent bubble walls of extrusive igneous rock. It is commonly,but not exclusively of silicic or felsic to intermediate in composition (e.g., rhyolitic, dacitic, andesite, pantellerite, phonolite, trachyte), but basaltic and other compositions are known. It is commonly pale in color, ranging from white, cream, blue or grey, to green-brown or black. It forms when volcanic gases exsolving from viscous magma form bubbles that remain within the viscous magma as it cools to glass. It is a common product of explosive eruptions (plinian and ignimbrite-forming) and commonly forms zones in upper parts of silicic lavas. It has a porosity of 64–85% by volume and it floats on water, possibly for years, until it is eventually waterlogged and sink.
There are two main forms of vesicles. Most of this rock contains tubular microvesicles that can impart a silky or fibrous fabric. The elongation of the microvesicles occurs due to ductile elongation in the volcanic conduit or, in the case of pumiceous lavas, during flow. The other form of vesicles are subspherical to spherical and result from high vapor pressure during eruption.
It is a unique rock, noted for its light weight and low density (dry pumice can float in water). It is commonly used in cement, concrete and breeze blocks and as an abrasive in polishes, pencil erasers, exfoliates and to produce stone-washed jeans. It is also used to remove dry skin from the bottom of the foot during the pedicure process at some beauty salons.
It is a very light weight, porous and abrasive material and it has been used for centuries in the construction and beauty industry as well as in early medicine.
It is also used as an
abrasive, especially in polishes, pencil erasers, and the production of
stone-washed jeans.
It was also used in the early book making industry to prepare parchment paper and leather bindings. There is high demand for pumice, particularly for water filtration, chemical spill containment, cement manufacturing, horticulture and increasingly for the pet industry.
References
Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
Atlas-hornin.sk. (2019). Atlas of magmatic rocks. [online] Available at: http://www.atlas-hornin.sk/en/home [Accessed 13 Mar. 2019].
Camptonite lamprophyre (Mesozoic, 100-200 Ma; Campton Falls, Grafton CountyOLYMPUS DIGITAL CAMERA
Lamprophyre is ultrapotassic igneous rock that is occurring as dikes, lopoliths, loccoliths, stocks and small intrussion. It is alkaline silica-undersaturated mafic or ultramafic rocks with high magnesium oxide, >3% potassium oxide, high sodium oxide and high nickel and chromium. Four minerals dominate these rocks: orthoclase, plagioclase, biotite, and hornblende. Amphibole and biotite tend to occur in a matrix of various combinations of plagioclase and other sodium- and potassium-rich feldspars, pyroxene, and feldspathoids.
In general, they form at great depth and are enriched in
sodium, cesium, rubidium, nickel, and chromium, as well as potassium, iron, and
magnesium. Some are also source rocks for diamonds. The exact origin of
lamprophyres is still debated. They form along the margins of some granites and
are often associated with large bodies of intrusive granodiorite.
Name origin: Lamprophyres
(Greek λαµπρός (lamprós) = “bright” and φύρω (phýro) = to mix)
Color: Dark brown
to black
Group: Extrusive
igneous rock
Minerals: Amphibole and biotite
tend to occur in a matrix of various combinations of plagioclase and other
sodium- and potassium-rich feldspars, pyroxene, and feldspathoids
Dominant Minerals: Orthoclase, plagioclase, biotite, and hornblende
Classification of lamprophyres has had several revisions and
so much argument within the geology. Modern naming has been derived from an
attempt some genetic parameters of lamprphyre genesis.This has, by and large,
dispensed with the previous provincial names of lamprophyre species, in favor
of a mineralogical name. The old names are still used for convenience.
Streckeisen recognized three main type of lamprophyres:
Calc-alkaline lamprophyres
Melilitic lamprophyres
Alkaline lamprophyres
Calc-Alkaline Lamprophyres
The calc-alkaline lamprophyres are also known as ordinary
lamprophyres and they consist of Minettes, Vosegites, Kersantites and
Spessartites. This lamprophyres are, in term of average chemical composition,
virtually indistinguishable.
Vogesite: Vogesite
was first described from the Vosges mountains, France, where rocks of this type
(actually, minette) were described in the early 20th century.
Minette: A dike
of minette near Shiprock, Navajo Volcanic Field. A historical view of minette
was provided by Johannsen (1937). He wrote that the name was ” … used by
the miners in the Vosges apparently for oolitic or granular iron ore, and
possibly derived from the valley of Minkette.
Spessartites:
From Spessart mountains east of Aschaffenburg in Germany. A spessartite is a
porphyritic alkaline igneous rock dominated by essential amphibole, usually
hornblende, and plagioclase feldspar, often with augite present as an
accessory. Plagioclase occurs in the groundmass and potassic feldspar is absent
or present in low abundance.
Kersantites: From
Kersanton, a village in France, are Plagioclase, Honrblende, Augite
lamprophyres.
Alkaline Lamprophyres And Melilitic Lamprophyres
The Alkaline and melilitic lamprophyres will be considered
together, because both groups contain alkaline rocks and are usually associated
with alkaline complexes and the rocks of the Carbonatite-nepheline-ijolite
association. The common alkaline lamprophyres are comptonites, Sannaites and
monchiquites and they are chemically akin to the alkaline basalt, basanites and
Nephelinites.
Comptonites: From
Campton in the New Hampshire (USA). A camptonite is a porphyritic alkaline
igneous rock dominated by essential plagioclase and brown amphibole, usually
hornblende, often with titanaugite. Plagioclase occurs in the groundmass.
Sannaites: From
Sannavand, Fen complex, Sweden. Sannaites are broadly to Comptonites, except
that they contain alkali feldspar in place of plagioclase.
Monchiquites:
From Sierra de Monchique in Southern Portugal. A monchiquite is a porphyritic
alkaline igneous rock dominated by essential olivine, titanaugite and brown
hornblende.
Alnöite: From
Alno island, Sweden. A alnöite is a porphyritic alkaline igneous rock dominated
by essential olivine, biotite and pyroxene, in a groundmass containing
melilite. It can contain monticellite.
Polenzite: From Polzen area of the Bohemian massif, Czechoslovakia.
Is a melilitic lamprophyre that usually contain between 10-30% of feldspathoids
(Nepheline and Hauyne) and it normally contains the same minerals as occur in
alnöite.
Lamprophyre Composition
Lamprophres is all term for ultrapotassic mafic igneous
rocks which have primary mineralogy consisting of amphibole or biotite, and
with feldspar in the groundmass. Four minerals dominate these rocks: orthoclase,
plagioclase, biotite, and hornblende. Amphibole and biotite tend to occur in a matrix
of various combinations of plagioclase and other sodium- and potassium-rich
feldspars, pyroxene, and feldspathoids. Because of their relative rarity and
varied composition, lamprophyres do not fit into standard geological
classifications. In general, they form at great depth and are enriched in
sodium, cesium, rubidium, nickel, and chromium, as well as potassium, iron, and
magnesium. Some are also source rocks for diamonds.
Lamprophyre Formation
In all geological periods, lamprophy occurs. Archaic
examples are usually associated with gold reserves. Among the Cenozoic
examples, the magnesian rocks in Mexico and South America and the young
ultramafic lamp lamps from Gympie in Australia are 18.5% MgO at ~ 250 Ma.
Rock lamps thought to be rock are part of a “clan”
of rocks with similar mineralogy, textures and formations. Lamprofiller,
lamproite and kimberlites. While modern concepts see orange, lampogens and
kimberlites separately, the vast majority of the lamprophytes have similar
origins to these other rock species.
Mitchell considers the lamprophytes as a “facies”
of magmatic rocks created by a number of conditions (usually; late, high
volatile differences of other rock species). Both schemes can be applied to all
and some of the large rock group known as lamprophyres and melilitic rocks.
Leaving aside the complex petrogenetic arguments, the basic
components in the formation of lamprophyre;
high depth of melting, which yields more mafic
magmas;
low degrees of partial melting, which yields
magmas rich in the alkalis (particularly potassium);
lithophile element (K, Ba, Cs, Rb) enrichment,
high Ni and Cr,
high potassium and sodium concentrations (silica
undersaturation is common)
some form of volatile enrichment, to provide the
biotite (phlogopite) and amphibole (pargasite) mineralogy
lack of fractional crystallisation (generally;
there are exceptions)
high Mg# ( MgO/(FeO + MgO) )
Individual examples thus may have a wide variety
of mineralogy and mechanisms for formation. Rock considered lamprophyres to be
derived from deep, volatile-driven melting in a subduction zone setting. Others
such as Mitchell consider them to be late offshoots of plutons, etc., though
this can be difficult to reconcile with their primitive melt chemistry and
mineralogy.
Where is the Lamprophyre Rock
Lamprophyres are usually associated with voluminous granodiorite
intrusive episodes. They occur as marginal facies to some granites, though
usually as dikes and sills marginal to and crosscutting the granites and
diorites. In other districts where granites are abundant no rocks of this class
are known. It is rare to find only one member of the group present, but
minettes, vogesites, kersantites, etc., all appear and there are usually
transitional forms.
Non-melilitic lamprophyres are found in many districts where
granites and diorites occur, such as the Scottish Highlands and Southern
Uplands of Scotland; the Lake District of northwest England; Ireland; the
Vosges Mountains of France; the Black Forest and Harz mountain regions of
Germany; Mascota, Mexico; Jamaica[8] and in certain locations of British
Columbia, Canada.
Economic Importance
The economic
importance of ultrapotassic rocks is wide and varied. Kimberlites, lamproites
and perhaps even lamprophyres are known to contain diamond. These rocks are all
produced at depths in excess of 120 km and thus can bring diamond to the
surface as xenocrysts. Ultrapotassic granites are a known hos for much
granite-hosted gold mineralisation. Significant porphyry-style mineralisation
is won from highly potassic to ultrapotassic granites. Ultrapotassic A-type
intracontinental granites may be associated with fluorite and
columbite-tantalite mineralization.
Conclusion
Lamprophyres
are melanocratic, porphyritic, hypabyssal rocks
The
lamprophyres commonly consists of alkali rich calc-alkali to ultramafic
minerals
The
economic importance of ultrapotassic rocks are wide and varied.
References
Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
Wikipedia contributors. (2019, March 14). Lamprophyre. In Wikipedia, The Free Encyclopedia. Retrieved 19:30, May 11, 2019, from https://en.wikipedia.org/w/index.php?title=Lamprophyre&oldid=887734669
Vale, L. (2019). ALEX STREKEISEN-Sannaite-. Alexstrekeisen.it. Available at: http://www.alexstrekeisen.it/english/vulc/sannaite.php [Accessed 11 May 2019].
