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)

Color: black or dark brown

Cooling Rate: rapid, extrusive

Intrusive Equivalent: diorite or gabbro

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

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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.

Physical Properties of Scoria

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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. Fracture: Scoria generally exhibits a rough and irregular fracture pattern, consistent with its porous and vesicular nature.
9. 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.
10. Water Absorption: Scoria’s porosity allows it to absorb and retain water, which can be advantageous in certain gardening and horticultural applications.
11. 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.
12. 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

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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. Erosion Control: Scoria can be used to stabilize slopes and prevent erosion in certain landscapes.
10. 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.
11. Geological and Educational Displays: Scoria samples are often used in geological displays and educational settings to showcase volcanic processes and rock types.
12. 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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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:

1. 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.
2. 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.
3. 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

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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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 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:

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. Art and Aesthetics: Scoria’s texture and color make it suitable for artistic and decorative purposes, including sculptures, mosaics, and architectural embellishments.
10. 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)

Composition: felsic (rhyolitic)

Color: white to light-gray or light-tan

Cooling Rate: rapid, extrusive

Intrusive Equivalent: granite

Other Characteristics: very light and will float on water

Minerals: Feldspar, augite, hornblende, zircon

Pumice Composition

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.

Physical Properties

Chemical Analysis (typical averages)

Pumice Uses

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].
• Helmenstine, Anne Marie, Ph.D. (2019, March 10). What Is Pumice Rock? Geology and Uses. Retrieved from https://www.thoughtco.com/pumice-rock-4588534

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

Lamprophyre Classification

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].

Pyroxenite is an ultramafic igneous rock that contain pyroxene group minerals such as augite, diopside, hypersthene, bronzite or enstatite. This is a coarse-grained rock and that contains at least 90 percent pyroxene minerals. Also Pyroxenite contain olivine and oxide minerals, when it occurs in layered intrusions or nepheline. It is hard and heavy rock and color is light green. Single crystals may be 3 inc or more in lenght. Pyroxenites are usually found with gabbros and peridotites. There are three type of pyroxenite rock that areclinopyroxenites, orthopyroxenites, and the websterites.

Color: Light green, dark green, or black

Protolith or Parent Rock:

Hardness: 5 to 7

Grain size: Coarse-grained texture

Group: Ultramafic igneous rock

Alterations: Crystallization of a silica-poor magma in a major intrusion

Minerals: Pyroxene, Biotite, hornblende, olivine, plagioclase, nepheline

Dominant Minerals: Pyroxene

Pyroxenite Classification

There are three type of pyroxenite rock that areclinopyroxenites, orthopyroxenites, and the websterites.

Orthopyroxene

Orthopyroxene partitions nickel, cobalt, and manganese less than olivine and there are no clear correlations amongst these elements. Although low in abundance, orthopyroxene can be a significant reservoir for the trivalent cations vanadium, scandium plus tetravalent titanium, due to its high modal abundance, especially in depleted xenoliths with little or no clinopyroxene. The abundances of strontium, niobium, zirconium, and yttrium in orthopyroxenes are near or below the ppm-level and show no clear correlations. A general feature is enrichment of titanium, zirconium, and niobium relative to coexisting clinopyroxene. The few measurements of the REE patterns in orthopyroxene are typically LREE-depleted, with all REE one to two orders of magnitude below clinopyroxene. There is far more scatter and far less coherent variation amongst many incompatible trace elements in orthopyroxene, likely reflecting more heterogeneity on the micro-scale as well as temperature effects that are not well understood with the paucity of data available (D.G.Pearson.,D.Canil.,S.B.Shirey, 2003 )

Clinopyroxene

Clinopyroxene is a major host for sodium, calcium, chromium, and titanium in mantle xenoliths and shows extensive solid solution toward orthopyroxene and/or garnet at high P and T in the mantle (Boyd, 1969, 1970; Brey and Köhler, 1990). The Mg# of clinopyroxene is usually slightly greater than that of coexisting olivine, due to a KD greater than 1. The calcium content of clinopyroxene is strongly T-dependent and is between 40 mol.% and 50 mol.% wollastonite component. Subcalcic clinopyroxenes (Wo<35%) occur in cratonic suites as megacrysts or discrete nodules, and indicate very high T of equilibration, perhaps in equilibrium with melt
D.G.Pearson.,D.Canil.,S.B.Shirey (2003) .

Websterite

Websterite is ultramafic igneous rock that consists of roughly equal proportions of orthopyroxene and clinopyroxene. It is a type of pyroxenite.

Pyroxenite Composition

Pyroxenite composition is contain at least 90 percent pyroxene group minerals, such as as augite, diopside, hypersthene, bronzite or enstatite.Pyroxenite also contain olivine and oxide minerals. Pyroxenite has less olivine than peridotites. The principal minerals usually found accompanying pyroxenites, in addition to olivine and feldspar, are chromite and other spinels, garnet, rutile, and magnetite. It has been proposed that large volumes of pyroxenite form in the upper mantle. Rare metamorphic pyroxenites are known and are described as pyroxene hornfels.

Where is the Pyroxenite Located

They frequently occur in the form of dikes or segregations in gabbro and peridotite: in Shetland, Cortland on the Hudson River, North Carolina (websterite), Baltimore, New Zealand, and in Saxony. They are also found in the Bushveld Igneous Complex in South Africa and Zimbabwe.

Classification diagram for peridotite and pyroxenite, based on proportions of olivine and pyroxene. The pale green area encompasses the most common compositions of peridotite in the upper part of the Earth’s mantle

The pyroxenites are often subject serpentinization under low temperature retrograde metamorphism and weathering. The rocks are often completely replaced by serpentines, which sometimes preserve the original structures of the primary minerals, such as the lamination of hypersthene and the rectangular cleavage of augite. Under pressure-metamorphism hornblende is developed and various types of amphibolite and hornblende-schist are produced. Occasionally rocks rich in pyroxene are found as basic facies of nepheline syenite; a good example is provided by the melanite pyroxenites associated with the borolanite variety found in the Loch Borralan igneous complex of Scotland.

Pyroxenite Uses

• Countertops, Decorative Aggregates, Interior Decoration, Kitchens
• As Building Stone, As Facing Stone
• Curbing
• As Dimension Stone, Building houses or walls, Cement Manufacture, Construction Aggregate, for Road Aggregate
• Cemetery Markers, Commemorative Tablets, Laboratory bench tops, Jewelry, Sea Defence, Tombstones

References

• Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
• D.G.Pearson.,D.Canil.,S.B.Shirey (2003) Mantle Samples Included in Volcanic Rocks: Xenoliths and Diamonds, Available online 7 June 2004, https://doi.org/10.1016/B0-08-043751-6/02005-3