Gold

Gold has been the most prized metal that is a chemical element with the symbol Au. It is opaque, has a highly attractive metallic golden yellow color, is extremely malleable, and is usually found in a relatively pure form. It is remarkably inert, so it resists tarnish. These qualities have made it exceptionally valuable. It usually occurs as treelike growths, grains, and scaly masses. It rarely occurs as well-formed crystals, but when found these are octahedral or dodecahedral. It is mostly found in hydrothermal veins with quartz and sulfides. Virtually all granitic igneous rocks in which it occurs as invisible, disseminated grains contain low concentrations of gold. Almost all of the gold recovered since antiquity has come from placer deposits weathered gold particles concentrated in river and stream gravel.

Chemically, it is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. It often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits.

A total of 186,700 tonnes of gold exists above ground, as of 2015. The world consumption of new gold produced is about

50% in jewelry,
40% in investments,
and 10% in industry.

Name: An Old English word for the metal; perhaps related to the Sanskrit jval; chemical symbol from the Latin aurum, shining dawn.

Association: Pyrite, chalcopyrite, arsenopyrite, pyrrhotite, sylvanite, krennerite, calaverite, altaite, tetradymite, scheelite, ankerite, tourmaline, quartz.

Polymorphism & Series: Forms a series with silver.

Cell Data: Space Group: Fm3m. a = 4.0786 Z = 4

These unique properties of gold make it a highly valuable and versatile metal that has been used for various purposes throughout human history, including as currency, jewelry, decorative items, and in various industrial applications.

Contents

Gold Associate Minerals
Gold Characteristics
Gold Physical Properties
Gold Chemical and Optical Properties
Chemical properties of gold
Optical properties of gold
Origins
Mining and Extraction of Gold
Gold Occurrence
Gold Production
Uses Area
Global Distribution
Key Points
References

Gold Associate Minerals

Gold is often found associated with other minerals in nature. Some common gold-associated minerals include:

Quartz: Quartz is a common mineral that is often associated with gold. It can occur in various forms, such as veins, stockworks, or as host rock in gold-bearing deposits. Quartz can serve as an indicator mineral for the presence of gold, as gold often forms within quartz veins.
Pyrite: Pyrite, also known as “fool’s gold,” is a common iron sulfide mineral that is often associated with gold deposits. Pyrite can occur in the same rock formations as gold and is sometimes mistaken for gold due to its similar appearance. However, unlike gold, pyrite does not contain any significant amounts of gold and is not economically valuable.
Arsenopyrite: Arsenopyrite is a mineral that contains both arsenic and iron and is often associated with gold deposits. It can occur in gold-bearing veins and is sometimes found along with gold in ores. Arsenopyrite can also serve as an indicator mineral for the presence of gold in certain geological settings.
Chalcopyrite: Chalcopyrite is a common copper iron sulfide mineral that can sometimes be associated with gold deposits. It can occur in the same rock formations as gold and may be present in ores that contain both copper and gold.
Galena: Galena is a common lead sulfide mineral that can sometimes be associated with gold deposits. It can occur in the same rock formations as gold and may be present in ores that contain both lead and gold.
Sphalerite: Sphalerite is a common zinc sulfide mineral that can occasionally be associated with gold deposits. It can occur in the same rock formations as gold and may be present in ores that contain both zinc and gold.
Other minerals: Other minerals that can be associated with gold include mica, hematite, magnetite, sericite, and various sulfides, oxides, and silicates. The presence of these minerals can sometimes indicate the potential for gold mineralization in a given geological setting.
Calcite: Calcite is a common calcium carbonate mineral that can sometimes be associated with gold deposits. It can occur in the same rock formations as gold and may be present in ores that contain both calcite and gold.
Tellurides: Telluride minerals, such as calaverite (gold telluride) and sylvanite (gold-silver telluride), are rare minerals that can be associated with gold deposits. They are often found in hydrothermal veins and can be indicators of high-grade gold mineralization.
Native silver: Native silver, which is silver in its pure elemental form, can sometimes be associated with gold deposits. It can occur in the same rock formations as gold and may be present in ores that contain both silver and gold.
Electrum: Electrum is a natural alloy of gold and silver, typically containing varying proportions of both metals. It is often found associated with gold deposits and can occur in the same rock formations as gold.
Bismuthinite: Bismuthinite is a bismuth sulfide mineral that can sometimes be associated with gold deposits. It can occur in the same rock formations as gold and may be present in ores that contain both bismuth and gold.
Stibnite: Stibnite is an antimony sulfide mineral that can occasionally be associated with gold deposits. It can occur in the same rock formations as gold and may be present in ores that contain both antimony and gold.
Quartz-sulfide veins: Quartz-sulfide veins, also known as “gold-bearing quartz veins,” are common features in many gold deposits. These veins are typically composed of quartz, sulfide minerals, and other minerals, including those mentioned above, and can be important indicators of gold mineralization.
Skarns: Skarns are contact metamorphic rocks that can be associated with gold deposits. They are typically formed in the contact zone between intrusive igneous rocks and carbonate-rich rocks, and can contain various minerals, including gold-associated minerals such as pyrite, chalcopyrite, and others.

It’s important to note that the presence of these minerals does not guarantee the presence of economically viable gold deposits. The occurrence of gold and its associated minerals depends on complex geological processes and the specific characteristics of each deposit. Detailed exploration and analysis are typically required to determine the economic viability of gold deposits and the potential for gold extraction.

Gold Characteristics

Gold from Oriental mine, Sierra Co., California, United States – RW47811

It is the most malleable of all metals. A single gram of gold can be beaten into a sheet of 1 square meter, and an avoirdupois ounce into 300 square feet. It leaf can be beaten thin enough to become semi-transparent. It is a good conductor of heat and electricity.

It has a density of 19.3 g/cm3, almost identical to that of tungsten at 19.25 g/cm3; as such, tungsten has been used in counterfeiting of gold bars, such as by plating a tungsten bar with gold, or taking an existing gold bar, drilling holes, and replacing the removed gold with tungsten rods.

Gold (Au) is a chemical element with the atomic number 79 and the symbol Au, derived from the Latin word “aurum”. It is a precious metal and is known for its unique properties, including:

Malleability and ductility: Gold is highly malleable, which means it can be hammered into thin sheets without breaking. It is also highly ductile, which means it can be drawn into thin wires without breaking. These properties make gold easy to shape and manipulate, allowing for intricate goldsmithing and jewelry making.
Density: Gold is a dense metal, with a density of approximately 19.3 grams per cubic centimeter (g/cm³). This high density makes gold feel heavy when held, and it also gives gold its characteristic “heft” or weight.
High melting and boiling point: Gold has a high melting point of approximately 1,064 degrees Celsius (1,947 degrees Fahrenheit) and a high boiling point of approximately 2,970 degrees Celsius (5,378 degrees Fahrenheit). This high melting and boiling point make gold resistant to heat and enable it to be used in various high-temperature applications, such as in electronics and aerospace industries.
Yellow color: Gold is known for its distinct yellow color, which gives it its aesthetic appeal and has made it highly desirable for jewelry and decorative purposes. However, gold can also occur in other colors, such as white, rose, and green, depending on the presence of other metals or impurities.
Non-reactivity: Gold is a relatively unreactive metal, meaning it does not tarnish, corrode, or rust easily. This makes gold highly durable and resistant to environmental degradation, which is one of the reasons why it has been used for jewelry and decorative purposes for thousands of years.
Excellent electrical conductivity: Gold is an excellent conductor of electricity, making it highly valuable in various electronic applications, such as in wiring, contacts, and connectors. Its high electrical conductivity, coupled with its resistance to corrosion, makes gold ideal for use in electronic devices where reliable and durable electrical connections are required.
Rarity: Gold is a relatively rare element in the Earth’s crust, with an average abundance of about 0.005 parts per million (ppm). This rarity adds to its value and makes it a precious metal that has been used as a store of value and medium of exchange for thousands of years.

Gold Physical Properties

Color	Rich yellow, paling to whitish-yellow with increasing silver; blue & green in transmitted light (only thinnest folia [gold leaf])
Streak	Shining yellow
Luster	Metallic
Cleavage	None Observed None
Diaphaneity	Opaque
Mohs Hardness	2.5 to 3
Crystal System	Isometric
Tenacity	Malleable
Density	15 – 19.3

Gold Chemical and Optical Properties

Chemical properties of gold

Chemical symbol: Au (from the Latin word “aurum”).
Atomic number: 79.
Atomic weight: 196.96657 u (unified atomic mass unit).
Gold is a noble metal, which means it is unreactive and does not easily tarnish, corrode, or oxidize.
Gold has a relatively low reactivity with most chemicals, acids, and gases, which contributes to its high resistance to corrosion and tarnish.

Optical properties of gold

Color: Gold is typically known for its distinctive yellow color, which is due to its unique electron configuration that results in the absorption and reflection of certain wavelengths of light. However, gold can also occur in other colors, such as white, rose, and green, depending on the presence of other metals or impurities.
Luster: Gold has a bright, metallic luster, which gives it a shiny and reflective appearance.
Transparency: Gold is opaque, which means it does not allow light to pass through.
Refractive index: Gold has a relatively low refractive index, which means it does not bend or deflect light significantly.
Reflectivity: Gold has a very high reflectivity for both visible and infrared light, making it highly useful in various optical applications, such as in mirrors and coatings for infrared optics.

These chemical and optical properties of gold contribute to its unique appearance and make it highly valuable and desirable for various applications, including jewelry, decorative items, and optical and electronic devices.

Origins

The origins of gold can be traced back to various geological processes and events. Here are some of the key origins of gold:

Supernovae: Gold is thought to form during supernova explosions, which are powerful stellar explosions that occur when massive stars reach the end of their life cycle and collapse under their own gravitational pull. During a supernova explosion, heavy elements, including gold, are synthesized through nuclear reactions in the intense heat and pressure generated by the explosion. These heavy elements are then dispersed into space and can later become part of new star systems and planets, including Earth.
Neutron star collisions: Another possible origin of gold is the collision of neutron stars, which are the incredibly dense remnants of massive stars that have gone supernova. When two neutron stars collide, they release a tremendous amount of energy and heat, causing the production of heavy elements, including gold, through rapid neutron capture processes known as r-process nucleosynthesis.
Hydrothermal processes: Gold can also form through hydrothermal processes, where hot, mineral-rich fluids are circulated through cracks and fractures in the Earth’s crust. As these fluids cool and deposit their mineral content, including gold, in the fractures, veins, or other rock formations. Over time, geological processes, such as erosion and tectonic movements, can bring these gold-bearing rocks to the Earth’s surface.
Placer deposits: Placer deposits are another common source of gold. Placer deposits are formed when gold is eroded from its original source rock and transported by water, such as rivers and streams. The gold particles settle in riverbeds, sandbars, or other areas of low energy flow, where they accumulate over time. Placer deposits are often mined through placer mining, which involves extracting gold particles from the sediment using various methods, such as panning, sluicing, and dredging.
Magmatic processes: In some cases, gold can also be associated with igneous rocks and form through magmatic processes. Gold can be transported by magma from deep within the Earth’s crust and deposited in cracks, veins, or other rock formations as the magma cools and solidifies. These gold-bearing rocks can later be exposed at the Earth’s surface through erosion, tectonic movements, or volcanic activities.

These are some of the main origins of gold, which involve various geological processes and events over millions of years. The complex geology and formation of gold deposits contribute to its rarity and high value as a precious metal.

Mining and Extraction of Gold

Mining and extraction of gold involve several methods, depending on the type and location of the gold deposit. Here are some common methods used in the mining and extraction of gold:

Open-pit Mining: Open-pit mining is a method used to extract gold from large, near-surface deposits. It involves the removal of overlying soil, rock, and vegetation to expose the gold-bearing ore. Once the ore is exposed, it is drilled, blasted, and transported to a processing plant for further extraction.
Underground Mining: Underground mining is used to extract gold from deeper deposits that are not accessible through open-pit mining. This method involves the construction of underground tunnels and shafts to access the gold-bearing ore. Underground mining can be more costly and complex compared to open-pit mining, but it may be necessary for extracting gold from deep or narrow deposits.
Placer Mining: Placer mining is a method used to extract gold from alluvial deposits, such as rivers, streams, and floodplains. It involves the use of water to separate gold particles from other sediments and materials. Placer mining can involve simple techniques such as panning, sluicing, and dredging, or more complex methods such as hydraulic mining and bucket-line dredging.
Cyanide Leaching: Cyanide leaching is a commonly used method for extracting gold from gold-bearing ores. It involves the use of a weak solution of sodium cyanide to dissolve the gold particles from the ore, which is then collected and processed to recover the gold. Cyanide leaching is a complex and controversial method due to its potential environmental and health risks, and strict regulations and safety measures are in place to minimize these risks.
Carbon-in-Pulp (CIP) and Carbon-in-Leach (CIL): CIP and CIL are modern methods used to extract gold from ore by adsorbing gold onto activated carbon particles. The ore is crushed, ground, and mixed with water, and a weak solution of sodium cyanide is added. The gold particles bond with the activated carbon, and the resulting gold-loaded carbon is then separated from the ore slurry and further processed to recover the gold.
Refining: Once gold has been extracted from the ore, it may require further refining to produce pure gold. Refining methods include smelting, where gold is melted and impurities are removed, and electrolysis, where an electric current is used to separate gold from other metals. Refining processes are used to produce gold bullion, which is the form of gold that is typically used for investment, jewelry, and other applications.

Mining and extraction of gold involve complex processes that require careful planning, environmental considerations, and safety measures to minimize environmental impacts and protect the health and safety of workers. These methods may vary depending on the characteristics of the gold deposit and the regulations and practices in the specific mining location.

Gold Occurrence

Native gold in vein, hosted by quartz. Photo is about 2 cm across.

Gold occurs in a wide range of geological settings and can be found in various types of deposits around the world. Here are some common occurrences of gold:

Quartz Veins: One of the most common occurrences of gold is in quartz veins. Gold-bearing quartz veins are formed when gold-rich hydrothermal fluids, typically associated with hot, mineral-rich fluids, are deposited in fractures and cracks in the Earth’s crust. Over time, these fluids cool and the gold particles precipitate out and accumulate in the quartz veins. Quartz veins are often mined for gold using underground or open-pit mining methods.
Placer Deposits: Placer deposits are another common occurrence of gold. Placer deposits are formed when gold is eroded from its original source rock and transported by water, such as rivers and streams. Gold particles settle in riverbeds, sandbars, or other areas of low energy flow, where they accumulate over time. Placer deposits can be found in rivers, streams, alluvial plains, and beach sands, and are often mined using placer mining methods, such as panning, sluicing, and dredging.
Witwatersrand Basin: The Witwatersrand Basin in South Africa is one of the world’s largest gold occurrences and has been a major source of gold production for over a century. The gold in the Witwatersrand Basin is found in conglomerate rock formations, known as “reefs,” which were formed in ancient sedimentary basins during the Archean Eon. The gold particles are often very small and finely disseminated throughout the conglomerate rock, and mining methods such as underground mining are used to extract the gold.
Carlin-Type Deposits: Carlin-type deposits are a unique type of gold occurrence that is found in Nevada, USA, and some other parts of the world. These deposits are characterized by the presence of microscopic gold particles that are disseminated throughout large volumes of sedimentary rock, often in limestone or dolomite formations. Carlin-type deposits are typically mined using open-pit mining methods and complex extraction techniques, such as heap leaching and carbon-in-pulp (CIP) processing.
Epithermal Deposits: Epithermal deposits are another type of gold occurrence that is typically found in volcanic regions. These deposits are formed when hot, mineral-rich fluids are released from volcanic activity and interact with surrounding rocks, leading to the deposition of gold and other minerals in veins, stockworks, or disseminated form. Epithermal deposits are often mined using underground mining methods.
Archean Greenstone Belts: Archean greenstone belts, which are found in various parts of the world, are known for their gold occurrences. These belts are ancient volcanic and sedimentary rock formations that were formed during the Archean Eon and are often associated with gold deposits. Gold in greenstone belts can occur in various forms, such as quartz veins, disseminated gold, and sulfide-hosted gold, and mining methods such as underground mining are used to extract the gold.

These are some of the common occurrences of gold, but gold can also be found in other types of deposits, such as alluvial deposits, breccia pipes, skarn deposits, and more. The occurrence of gold is influenced by various geological processes, including hydrothermal activity, erosion, and tectonic movements, and the type of gold deposit can vary greatly depending on the geological setting.

Gold Production

Gold production refers to the process of extracting gold from its ore or deposits and refining it to obtain pure gold. Here are some key points related to gold production:

Mining: Gold is typically mined from gold-bearing deposits using various methods, such as underground mining, open-pit mining, placer mining, and heap leaching. The choice of mining method depends on factors such as the location, size, and grade of the gold deposit, as well as economic, environmental, and social considerations.
Ore Processing: Once gold-bearing ore is extracted from the ground, it is usually processed to extract the gold particles. Ore processing methods can vary depending on the type of gold deposit, but commonly include crushing, grinding, gravity separation, flotation, and cyanide leaching. These processes aim to separate gold from other minerals and impurities in the ore.
Refining: After the gold is extracted from the ore, it is often further processed to refine it to a higher level of purity. Refining methods can include smelting, electrolysis, and chemical processes, such as the Miller and Wohlwill processes, which use heat, electricity, and chemicals to remove impurities and obtain pure gold.
Gold Production Statistics: Gold production is a significant industry worldwide, and production levels can vary from year to year and from country to country. Some of the top gold-producing countries include China, Australia, Russia, the United States, Canada, and South Africa. Gold production is influenced by factors such as gold prices, technological advancements, mining regulations, environmental considerations, and geopolitical factors.
Artisanal and Small-scale Gold Mining (ASGM): In addition to large-scale industrial gold production, there is also a significant amount of gold production that occurs through artisanal and small-scale gold mining (ASGM) in many parts of the world. ASGM involves the use of simple tools and techniques to extract gold from small deposits or alluvial deposits, often in remote or rural areas. ASGM can have significant social, economic, and environmental impacts, and efforts are being made to improve the sustainability and safety of ASGM practices.
Gold Recycling: Gold can also be obtained through recycling of gold-containing products, such as electronic waste, jewelry, and industrial waste. Recycling gold helps to reduce the demand for newly mined gold and can contribute to the conservation of natural resources and reduction of environmental impacts associated with gold mining.

Overall, gold production involves the extraction, processing, and refining of gold from its ore or deposits, and it is influenced by various factors such as the type of deposit, mining methods, refining processes, production statistics, and sustainability considerations.

Uses Area

It has been widely used throughout the world as money, for efficient indirect exchange (versus barter), and to store wealth in hoards. For exchange purposes, mints produce standardized gold bullion coins, bars and other units of fixed weight and purity.
After World War II it was replaced by a system of nominally convertible currencies related by fixed exchange rates following the Bretton Woods system. Gold standards and the direct convertibility of currencies to gold have been abandoned by world governments, led in 1971 by the United States’ refusal to redeem its dollars in gold. Fiat currency now fills most monetary roles. Switzerland was the last country to tie its currency to gold; it backed 40% of its value until the Swiss joined the International Monetary Fund in 1999.
Central banks continue to keep a portion of their liquid reserves as gold in some form, and metals exchanges such as the London Bullion Market Association still clear transactions denominated in gold, including future delivery contracts.
It has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties.
The ISO 4217 currency code of gold is XAU. Many holders of gold store it in form of bullion coins or bars as a hedge against inflation or other economic disruptions, though its efficacy as such has been questioned; historically, it has not proven itself reliable as a hedging instrument.

Jewelry

Because of the softness of pure (24k), it is usually alloyed with base metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties.

Electronics

Only 10% of the world consumption of new gold produced goes to industry,[8] but by far the most important industrial use for new gold is in fabrication of corrosion-free electrical connectors in computers and other electrical devices.
Though it is attacked by free chlorine, its good conductivity and general resistance to oxidation and corrosion in other environments (including resistance to non-chlorinated acids) has led to its widespread industrial use in the electronic era as a thin-layer coating on electrical connectors, thereby ensuring good connection. For example, it is used in the connectors of the more expensive electronics cables, such as audio, video and USB cables.
Besides sliding electrical contacts, it is also used in electrical contacts because of its resistance to corrosion, electrical conductivity, ductility and lack of toxicity.

Medicine

Metallic and compounds have long been used for medicinal purposes. It, usually as the metal, is perhaps the most anciently administered medicine (apparently by shamanic practitioners) and known to Dioscorides.
In the 19th century gold had a reputation as a “nervine”, a therapy for nervous disorders. Depression, epilepsy, migraine, and glandular problems such as amenorrhea and impotence were treated, and most notably alcoholism (Keeley, 1897, Wikipedia).
It alloys are used in restorative dentistry, especially in tooth restorations, such as crowns and permanent bridges. The gold alloys’ slight malleability facilitates the creation of a superior molar mating surface with other teeth and produces results that are generally more satisfactory than those produced by the creation of porcelain crowns. The use of gold crowns in more prominent teeth such as incisors is favored in some cultures and discouraged in others.
Gold, or alloys of gold and palladium, are applied as conductive coating to biological specimens and other non-conducting materials such as plastics and glass to be viewed in a scanning electron microscope.

Global Distribution

Gold is found in various parts of the world, with different regions having different levels of gold production. Some of the major gold-producing regions around the world include:

Witwatersrand Basin, South Africa: The Witwatersrand Basin in South Africa is one of the world’s largest and oldest gold mining regions, known for its rich gold deposits. It has been a major gold-producing area since the late 1800s and has produced over 40% of the world’s gold.
Carlin Trend, United States: The Carlin Trend in Nevada, United States, is one of the most significant gold-producing regions in North America. It is known for its large, low-grade gold deposits, and is home to several major gold mines operated by large mining companies.
Super Pit, Australia: The Super Pit in Western Australia is one of the largest open-pit gold mines in the world, producing significant amounts of gold. It is a joint venture between two mining companies and has been in operation since 1989.
Muruntau Mine, Uzbekistan: The Muruntau Mine in Uzbekistan is one of the largest open-pit gold mines in the world, known for its massive gold reserves. It has been in operation since the 1960s and is a significant source of gold production in Central Asia.
Yanacocha Mine, Peru: The Yanacocha Mine in Peru is one of the largest gold mines in South America, known for its open-pit mining operations. It has been in operation since the early 1990s and is a major contributor to Peru’s gold production.
Other Regions: Gold is also found in many other regions around the world, including Canada, Russia, China, Indonesia, Ghana, Papua New Guinea, and many countries in West Africa.

It’s important to note that the global distribution of gold deposits can change over time as new discoveries are made, mining technologies evolve, and economic and environmental factors impact production levels. Additionally, the accessibility and viability of gold deposits can vary depending on factors such as geological characteristics, infrastructure, regulations, and market conditions.

Key Points

Physical properties: Gold is a soft, yellow metal with a bright metallic luster. It is one of the least reactive chemical elements and does not tarnish or corrode. Gold has a high melting and boiling point, and is a good conductor of electricity and heat.
Occurrence: Gold is relatively rare in the Earth’s crust and is often found in small concentrations in rocks, soils, and water. It is usually found in association with other minerals, such as quartz, pyrite, and other sulfide minerals, and can be found in various types of geological formations, including veins, placers, and deposits associated with igneous, metamorphic, and sedimentary rocks.
Mining and extraction: Gold is typically mined from the Earth using various methods, such as placer mining, lode mining, and heap leaching. Once extracted, gold ore is processed to extract the gold metal using techniques such as crushing, grinding, gravity separation, and chemical processes like cyanidation.
Global distribution: Gold is found in many countries around the world, with the largest gold-producing countries including China, Russia, Australia, the United States, Canada, and South Africa. Gold deposits can be found on all continents, but they are often unevenly distributed and can vary greatly in size and quality.
Uses and applications: Gold has been used for various purposes throughout human history, including as a form of currency, jewelry, decoration, and investment. It is also used in a wide range of industrial applications, including in electronics, dentistry, aerospace, and medicine. Additionally, gold is used in many cultural and religious practices, and has symbolic and cultural significance in many societies.
Environmental considerations: Gold mining and extraction can have environmental impacts, including habitat destruction, water pollution, and soil erosion. Proper environmental management and regulatory measures are important to mitigate these impacts and ensure responsible gold mining practices.
Gold price and market: Gold is traded globally as a commodity and its price is subject to fluctuations in the international market. The demand for gold is influenced by various factors, including economic conditions, geopolitical events, and investor sentiment. Gold is often considered a safe haven asset and a hedge against inflation and currency fluctuations, and it plays an important role in global financial markets.

References

Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
Mindat.org. (2019). Orpiment: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
Smith.edu. (2019). Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].
Wikipedia contributors. (2019, May 19). Gold. In Wikipedia, The Free Encyclopedia. Retrieved 00:26, June 10, 2019, from https://en.wikipedia.org/w/index.php?title=Gold&oldid=897845459

Fumaroles, Yellowstone National Park

The story of Yellowstone’s thermal basins begins with features deep within the earth. At the center of the earth is the core which is surrounded by the mantle and finally the earths crust. But what interests us is a feature known as a hotspot. It is a source of immense heat anchored within the mantle. This same hotspot is responsible for volcanic active in a number of areas in southeast Idaho including Craters of the Moon National Monument. After millions of years of movement of the earths crust this hotspot now lies beneath Yellowstone.

About 600 thousand years ago this hotspot sent a column of hot magma toward the surface forming a huge magma chamber. As the magma chamber filled it pushed upward on the earths crust forming a large dome.

As pressure built on the surface, cracks formed around the edge of the dome and a huge eruption expelled a tremendous amount of magma emptying a large portion of the magma chamber.

With the removal of hundreds of cubic miles of molten rock, the roof of the dome collapsed in what was one of the most violent explosions the earth has ever known.

Lava continued to flow into the caldera for the next 500 thousand years filling much of crater. It is this still active volcanic area that provides the heat source for Yellowstone’s thermal features.

The Yellowstone region has produced three exceedingly large volcanic eruptions in the past 2.1 million years. In each of these cataclysmic events, enormous volumes of magma erupted at the surface and into the atmosphere as mixtures of red-hot pumice, volcanic ash (small, jagged fragments of volcanic glass and rock), and gas that spread as pyroclastic (“fire-broken”) flows in all directions. Rapid withdrawal of such large volumes of magma from the subsurface then caused the ground to collapse, swallowing overlying mountains and creating broad cauldron-shaped volcanic depressions called “calderas.”

The first of these caldera-forming eruptions 2.1 million years ago created a widespread volcanic deposit known as the Huckleberry Ridge Tuff, an outcrop of which can be viewed at Golden Gate, south of Mammoth Hot Springs. This titanic event, one of the five largest individual volcanic eruptions known anywhere on the Earth, formed a caldera more than 60 miles (100 km) across.

A similar, smaller but still huge eruption occurred 1.3 million years ago. This eruption formed the Henrys Fork Caldera, located in the area of Island Park, west of Yellowstone National Park, and produced another widespread volcanic deposit called the Mesa Falls Tuff.

The region’s most recent caldera-forming eruption 640,000 years ago created the 35-mile-wide, 50-mile-long (55 by 80 km) Yellowstone Caldera. Pyroclastic flows from this eruption left thick volcanic deposits known as the Lava Creek Tuff, which can be seen in the south-facing cliffs east of Madison, where they form the north wall of the caldera. Huge volumes of volcanic ash were blasted high into the atmosphere, and deposits of this ash can still be found in places as distant from Yellowstone as Iowa, Louisiana, and California.

Each of Yellowstone’s explosive caldera-forming eruptions occurred when large volumes of “rhyolitic” magma accumulated at shallow levels in the Earth’s crust, as little as 3 miles (5 km) below the surface. This highly viscous (thick and sticky) magma, charged with dissolved gas, then moved upward, stressing the crust and generating earthquakes. As the magma neared the surface and pressure decreased, the expanding gas caused violent explosions. Eruptions of rhyolite have been responsible for forming many of the world’s calderas, such as those at Katmai National Park, Alaska, which formed in an eruption in 1912, and at Long Valley, California.

If another large caldera-forming eruption were to occur at Yellowstone, its effects would be worldwide. Thick ash deposits would bury vast areas of the United States, and injection of huge volumes of volcanic gases into the atmosphere could drastically affect global climate. Fortunately, the Yellowstone volcanic system shows no signs that it is headed toward such an eruption. The probability of a large caldera-forming eruption within the next few thousand years is exceedingly low.

World’s Most Active Volcanoes

Active volcanoes are natural wonders that continuously shape and reshape our planet’s landscape. These geologic giants, scattered across various regions of the world, exhibit a persistent and ongoing pattern of volcanic activity. This activity can manifest as eruptions, lava flows, ash plumes, and other volcanic phenomena. The world’s most active volcanoes are renowned for their unpredictability and capacity to impact the environment, local communities, and even global climate.

Volcanic eruptions are the result of the movement of molten rock (magma) from beneath the Earth’s crust to the surface. When this magma reaches the surface, it can create spectacular displays of eruptive power, but it also poses potential hazards to those living in proximity. Monitoring and understanding these active volcanoes is crucial for the safety and well-being of communities nearby and for the broader scientific community, as the study of these volcanoes offers insights into Earth’s geologic processes.

In this series, we will delve into the world’s most active volcanoes, exploring their locations, histories, notable eruptions, and their impact on the surrounding regions. We will also discuss the measures in place to monitor and mitigate the risks associated with these volcanoes. From the fiery spectacle of Hawaii’s Kilauea to the snow-capped peaks of Italy’s Mount Etna, join us on a journey to discover the incredible geological forces that shape our planet and the resilient communities that call these volatile landscapes home.

Now we have made a list of the biggest volcanoes that have been active recently.The volcanoes below are considered especially dangerous due to latest eruptions or due to being included in the Decade Volcanoes list. The Decade Volcanoes list is a list of 16 volcanoes worldwide identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas.

Contents

Kilauea, Hawaii, USA
Mount Etna, Sicily, Italy
Pacaya, Guatemala
Eyjafjallajökull, Iceland
Mount Vesuvius, Italy
Sakurajima, Japan
Mount Merapi, Indonesia
Mount Nyiragongo, Congo
Ulawun, Papua New Guinea
Mauna Loa, Hawaii
Galeras, Colombia
Santa María, Guatemala

Kilauea, Hawaii, USA

Kilauea is an active shield volcano located on the Big Island of Hawaii, USA. It is renowned for its frequent eruptions, including the Pu’u ‘Ō’ō eruption that began in 1983 and continued for several decades, reshaping the island’s landscape. Kilauea’s eruptions often produce lava flows that can reach the ocean, creating dramatic steam and new land. The volcano is closely monitored by the Hawaiian Volcano Observatory to ensure the safety of the local population and visitors to Hawaii Volcanoes National Park.

Mount Etna, Sicily, Italy

Mount Etna, situated on the island of Sicily in Italy, is one of Europe’s most active and iconic volcanoes. Known for its frequent eruptions, Etna is a stratovolcano that has shaped the region’s landscape for millennia. Its eruptions often involve the spewing of ash, lava, and occasional pyrotechnic displays. As one of Italy’s most closely monitored volcanoes, Etna’s activity is of significant interest to scientists and poses both a natural wonder and a potential hazard to nearby communities.

Pacaya, Guatemala

Amazing volcano El Fuego during a eruption on the left and the Acatenango volcano on the right, view from Antigua, Guatemala

Pacaya is a highly active complex volcano located in Guatemala. With a history of frequent eruptions, it is renowned for its lava flows, Strombolian explosions, and a persistent threat to the surrounding region. The volcano attracts hikers and tourists eager to witness its volcanic activity. Given its proximity to populated areas, Pacaya’s eruptions are closely monitored to ensure the safety of local communities.

Eyjafjallajökull, Iceland

Icelandic for “Island mountain glacier”, this volcano is one of the smaller ice caps of Iceland. The ice cap covers the caldera of a volcano with a summit elevation of 1,666 meters (5,466 ft). The 2010 eruption caused enormous disruption to air travel across western and northern Europe. About 20 countries closed their airspace to commercial jet traffic and it affected more than 100,000 travelers

The eruption in 2010 started on March 20 and continued until May 23. It began with a series of small earthquakes, followed by an explosive eruption that sent a plume of ash and volcanic gases into the atmosphere. The ash cloud disrupted air travel across Europe for several days, as many flights were cancelled due to concerns about the potential damage that the ash could cause to jet engines.

The eruption also resulted in the evacuation of nearby communities due to the threat of flooding from meltwater caused by the melting of the glacier. Fortunately, there were no fatalities or serious injuries as a result of the eruption.

Eyjafjallajökull is considered to be one of the most active volcanoes in Iceland, with eruptions occurring every 200-400 years on average. It is closely monitored by scientists, who use a variety of techniques to study its activity and better understand its potential to impact the surrounding communities.

Mount Vesuvius, Italy

Mount Vesuvius is a stratovolcano located in southern Italy, near the city of Naples. It is perhaps best known for its devastating eruption in 79 AD that buried the cities of Pompeii and Herculaneum in ash and pumice, preserving them for centuries.

It the most densely populated volcanic region in the entire world. Mount Vesuvius has a history of activity that makes it one of the world’s most dangerous volcanoes. It last erupted was in 1944, but the most memorable eruption was the massive eruption of 79 AD, when it buried the cities of Herculaneum and Pompeii

The 79 AD eruption of Mount Vesuvius was one of the most catastrophic volcanic events in history. It is estimated to have released 100,000 times the thermal energy of the atomic bomb that was dropped on Hiroshima in 1945. The eruption sent a plume of ash and volcanic gases into the atmosphere that reached a height of over 20 miles, and buried the cities of Pompeii and Herculaneum under layers of ash and pumice.

Sakurajima, Japan

Sakurajima is an active volcano located on the southern Japanese island of Kyushu, in Kagoshima Bay. It is one of the most active volcanoes in Japan and is known for its frequent and sometimes violent eruptions.

An active volcano and a former island. The lava flows of the 1914 eruption caused the former island to be connected with the Osumi Peninsula. The volcanic activity still continues, dropping large amounts of volcanic ash on the surroundings. Earlier eruptions built the white sands highlands in the region

Since then, Sakurajima has continued to be active, with hundreds of small eruptions occurring each year. The volcano is closely monitored by scientists, who use a variety of techniques such as seismology, gas measurements, and satellite imaging to track its activity and provide warning of potential eruptions.

Mount Merapi, Indonesia

Mount Merapi is an active volcano located in central Java, Indonesia. It is one of the most active and dangerous volcanoes in Indonesia, with a long history of eruptions that have caused significant damage and loss of life. Mount Merapi is part of the Pacific Ring of Fire, a region of intense seismic and volcanic activity that encircles the Pacific Ocean

The most recent major eruption of Mount Merapi occurred in 2010, which caused significant damage and resulted in the deaths of more than 300 people. The eruption was also responsible for the displacement of tens of thousands of people who were forced to flee their homes due to the danger posed by the volcano.

Mount Nyiragongo, Congo

An active volcano located inside Virunga National Park, in the Democratic Republic of the Congo. The main crater is about two km wide and usually contains a lava lake. Nyiragongo’s lava lake has at times been the most voluminous known lava lake in recent history. Nyiragongo and nearby Nyamuragira are together responsible for 40% of Africa’s historical volcanic eruptions.

The volcano has erupted at least 34 times since the late 19th century, with the most recent eruption occurring in May 2021. The 2002 eruption was particularly devastating, as lava flows reached the city of Goma and destroyed over 15% of its buildings, resulting in the displacement of over 120,000 people.

Ulawun, Papua New Guinea

Ulawun is an active volcano located on the island of New Britain in Papua New Guinea. It is one of the most active and dangerous volcanoes in Papua New Guinea, with a long history of eruptions that have caused significant damage and loss of life. It is the highest mountain in the Bismarck Archipelago at 2,334 meters (7,657 ft), and one of the most active volcanoes in Papua New Guinea. Several thousand people live near the volcano. There have been 22 recorded eruptions since the 18th century.

The most recent major eruption of Ulawun occurred in 2019, which caused significant damage and forced the evacuation of nearby communities. The eruption also generated a large ash plume that disrupted air traffic in the region.

Mauna Loa, Hawaii

Mauna Loa is a massive shield volcano located on the Big Island of Hawaii, and is one of the largest active volcanoes on Earth. It is considered one of the most active volcanoes in the world, with a long history of frequent eruptions. The Hawaiian name “Mauna Loa” means “Long Mountain”. Lava eruptions from Mauna Loa are very fluid; eruptions tend to be non-explosive and the volcano has relatively shallow slopes. The most recent eruption of Mauna Loa occurred in 1984, and scientists continue to closely monitor the volcano for signs of activity.

Galeras, Colombia

Galeras is an active volcano located in the southwestern region of Colombia, near the city of Pasto. It is considered one of the most active volcanoes in Colombia. It summit rises 4,276 meters (14,029 ft) above sea level. It has erupted frequently since the Spanish conquest, with its first historical eruption being recorded on December 7, 1580. A 1993 eruption killed nine people, including six scientists who had descended into the volcano’s crater to sample gases. It is currently the most active volcano in Colombia. The most recent major eruption of Galeras occurred in 1993, which caused the deaths of several scientists and tourists who were inside the crater at the time of the eruption.

Santa María, Guatemala

Santa María is an active volcano located in the western highlands of Guatemala, near the city of Quetzaltenango. Its eruption in 1902 was one of the four largest eruptions of the 20th century and one of the five biggest eruptions of the past 200 years. The most recent major eruption of Santa María occurred in 1902, which was one of the most violent volcanic eruptions of the 20th century and caused the deaths of over 5,000 people.

Eye Of The Sahara or Richat Structure

The Eye of the Sahara, also known as the Richat Structure, is a geological formation located in the Sahara Desert near Ouadane, Mauritania. This unique and distinctive feature is a massive circular structure that spans approximately 30 miles (50 kilometers) in diameter. The structure’s concentric rings and symmetrical pattern give it the appearance of a giant bull’s-eye when viewed from above, hence the name “Eye of the Sahara.”

Location and Geography: The Eye of the Sahara is situated in the Adrar Plateau, a rocky region of Mauritania in northwestern Africa. Its coordinates are approximately 21°07’N latitude and 11°22’W longitude. The area is characterized by arid and desert conditions, making the Eye of the Sahara a stark contrast to the surrounding landscape. Despite its impressive size, the structure is not easily visible from the ground due to its relatively flat and featureless topography.

Discovery and Historical Significance: The Eye of the Sahara has likely been known to local populations for centuries, but it gained international attention with the advent of space exploration. When astronauts first observed it from space, they initially thought it might be a meteorite impact crater. However, subsequent research revealed its true geological nature.

From a historical perspective, the Eye of the Sahara has intrigued researchers due to its unique and captivating appearance. Its concentric rings and geological features have made it a subject of interest for scientists studying the Earth’s geological history and processes. The formation provides valuable insights into the planet’s geological evolution and the forces that have shaped its surface over millions of years.

In recent years, the Eye of the Sahara has also become a destination for scientific research and tourism, attracting geologists, researchers, and travelers interested in exploring its geological mysteries and appreciating its natural beauty.

Contents

Formation and Geological Features
Hypotheses on Formation
Age and Geological History
Scientific Research and Exploration
Tourism and Accessibility
Summary of Key Findings

Formation and Geological Features

(Photo credit: NASA / SPL / Barcroft Images / Barcroft Media via Getty Images)

The Eye of the Sahara, or Richat Structure, is believed to have formed over a prolonged period through a combination of geological processes, including uplift, erosion, and the exposure of various rock layers. The circular structure is not the result of a meteorite impact, as was initially hypothesized, but rather a product of natural geological forces.

Circular Structure: The most prominent feature of the Eye of the Sahara is its circular or bull’s-eye shape. This circular structure is characterized by a series of concentric rings, with the center of the formation being more elevated than the outer rings. The distinctive appearance is due to the erosion of resistant layers of rock that create a pattern of alternating ridges and troughs.

Diameter and Dimensions: The Eye of the Sahara is vast in scale, with an approximate diameter of around 30 miles (50 kilometers). The central peak, or dome, rises to an elevation of about 400 meters (1,300 feet) above the surrounding terrain. The overall dimensions of the structure make it clearly visible from space and contribute to its striking appearance when observed from above.

Layers and Rock Formations: The formation is composed of various layers of sedimentary rock, including limestone and shale, which have been deposited over millions of years. The alternating layers give the Eye of the Sahara its distinct ringed appearance. The rocks provide a record of the geological history of the region, with different layers representing different periods of sedimentation and environmental conditions.

Central Erosion and Symmetry: The central part of the Eye of the Sahara exhibits a significant degree of erosion, forming a circular structure with a raised central peak. Erosion has removed softer rock layers, leaving behind more resistant layers that now form concentric rings. The symmetry of the structure is notable, and this symmetry is a key feature that distinguishes it from impact craters, which often display asymmetry due to the direction of the impacting force.

The erosion process that shaped the Eye of the Sahara is ongoing, and it continues to be an area of interest for scientists studying landscape evolution and geological formations. Understanding the processes that have shaped this unique structure provides valuable insights into the geological history of the Earth.

Hypotheses on Formation

While the exact process of the Eye of the Sahara’s formation is not universally agreed upon, several hypotheses have been proposed by scientists. As of my last knowledge update in January 2022, these are some of the leading theories:

Erosion and Uplift: One widely accepted hypothesis suggests that the Eye of the Sahara is a result of erosion and uplift. The structure is believed to have formed as a result of the uplift of rock layers, possibly caused by magmatic activity or tectonic forces. Subsequent erosion by wind and water then sculpted the landscape, exposing the concentric layers of rock and creating the circular structure.
Anticline Formation: Another hypothesis proposes that the Eye of the Sahara is an eroded and exposed ancient geological structure known as an anticline. An anticline is a fold in rock layers that forms an arch-like shape. Over time, erosion may have removed the softer rock layers, leaving the more resistant layers to create the concentric ring pattern.
Salt Diapir Hypothesis: Some scientists have suggested that the Eye of the Sahara could be related to a salt diapir. A salt diapir forms when salt, due to its buoyancy, rises through overlying sedimentary rocks. This process could lead to the formation of a domed structure, and subsequent erosion would expose the concentric rings.
Impact Cratering (Less Likely): Although the impact hypothesis has been largely discounted, it was initially considered due to the circular shape of the structure. However, further geological studies have not provided evidence of shock metamorphism or other features typically associated with impact craters, leading scientists away from this explanation.

It’s important to note that these hypotheses are not mutually exclusive, and the formation of the Eye of the Sahara is likely the result of a combination of geological processes acting over an extended period. Ongoing research and advancements in geological studies may provide more insights and refine our understanding of how this unique structure came into existence. Scientists continue to investigate the Eye of the Sahara to unravel its geological history and the forces that shaped it.

Age and Geological History

Determining the precise age of the Eye of the Sahara, or Richat Structure, has proven to be a challenging task. As of my last knowledge update in January 2022, there hasn’t been a definitive age assigned to this geological formation. However, various geological studies and dating techniques have provided some insights into its age and history.

**1. Paleozoic Sediments: The rocks that make up the Eye of the Sahara include sedimentary layers dating back to the Paleozoic Era, which spans from around 541 million to 252 million years ago. These sedimentary rocks contain a record of environmental conditions and geological processes that occurred during that time.

**2. No Evidence of Impact: While the circular structure initially led to speculation about an impact origin, subsequent studies have not found evidence of shock metamorphism or other features typically associated with impact craters. This lack of impact-related characteristics has contributed to the consensus that the Eye of the Sahara formed through geological processes rather than a cosmic impact.

**3. Erosional History: The erosion and exposure of different rock layers within the structure provide a chronological record of geological events. The alternating layers of resistant and softer rocks suggest a complex history involving uplift, folding, and erosion over an extended period.

Geological formations like the Eye of the Sahara often pose challenges in terms of dating because traditional radiometric dating methods might not be applicable to sedimentary rocks or might provide broad ranges. Scientists might use a combination of dating techniques, including stratigraphy and the analysis of isotopes, to piece together the geological history.

Ongoing research and advancements in dating methods may provide more accurate age estimates for the Eye of the Sahara and further insights into the specific geological processes that shaped this remarkable structure. It’s recommended to check for more recent scientific publications or studies for any updates on the age and geological history of the Eye of the Sahara.

Scientific Research and Exploration

Scientific research and exploration of the Eye of the Sahara have been ongoing to unravel the geological mysteries surrounding this unique structure. Researchers from various fields, including geology, planetary science, and remote sensing, have contributed to our understanding of the Eye of the Sahara. Here are some aspects of scientific research and exploration related to this geological formation:

Geological Studies: Geologists have conducted detailed field studies and collected rock samples to analyze the composition and structure of the Eye of the Sahara. These studies aim to understand the geological processes that led to its formation, including the role of tectonic forces, uplift, and erosion.
Dating Techniques: Researchers employ various dating techniques to determine the age of the rocks within the structure. While radiometric dating may be challenging with sedimentary rocks, other methods, such as optically stimulated luminescence (OSL) dating or magnetostratigraphy, may provide valuable age constraints.
Remote Sensing and Satellite Imagery: Satellite imagery and remote sensing technologies have played a crucial role in studying the Eye of the Sahara. These tools provide a comprehensive view of the structure, allowing scientists to analyze its features, map geological formations, and monitor changes over time.
Geomorphological Studies: Geomorphologists study the landforms and surface features of the Eye of the Sahara to gain insights into the processes that shaped the landscape. This includes analyzing the distribution of sedimentary layers, erosional patterns, and the overall topography of the region.
Paleoclimate Research: The sedimentary rocks within the Eye of the Sahara hold clues about past climates and environmental conditions. Researchers analyze these rocks to reconstruct paleoclimatic conditions and understand how the Sahara region has evolved over geological time scales.
Tourism and Education: The Eye of the Sahara has become a destination for scientific tourism, attracting researchers, geologists, and students. Field trips and guided tours provide opportunities for hands-on learning and further exploration of the geological features of the region.

Scientific research on the Eye of the Sahara contributes not only to our understanding of Earth’s geological history but also has implications for studying similar features on other planets. The unique characteristics of this structure make it a valuable natural laboratory for exploring geological processes and landscape evolution. As research continues, new findings and insights may emerge, refining our understanding of this fascinating geological formation.

Tourism and Accessibility

The Eye of the Sahara has been relatively limited due to its remote location and the challenging conditions of the surrounding Sahara Desert. However, there has been a growing interest in the geological wonder, and efforts have been made to facilitate access for researchers, scientists, and tourists. Keep in mind that conditions and accessibility may have changed since then.

Accessibility:

Remote Location: The Eye of the Sahara is situated in the Adrar Plateau in Mauritania, and reaching the site can be challenging due to its remote location. The nearest town is Ouadane, and transportation to the area may involve off-road travel.
Travel Restrictions: Visitors to the region may need to navigate travel restrictions and obtain necessary permits to explore the area. The political and security situation in the region can also impact accessibility.

Tourism:

Scientific Tourism: The Eye of the Sahara has gained attention as a destination for scientific tourism. Researchers, geologists, and students interested in the unique geological features may visit the site for field studies and exploration.
Guided Tours: Some tour operators offer guided tours to the Eye of the Sahara. These tours often involve knowledgeable guides who can provide insights into the geological history of the formation.
Educational Programs: Educational programs may be organized to facilitate visits by students and researchers. These programs can include lectures, workshops, and hands-on experiences related to the geology of the region.

Challenges:

Harsh Climate: The Sahara Desert has a harsh climate with extreme temperatures, and visitors need to be prepared for the challenging conditions, including high temperatures during the day and cooler temperatures at night.
Limited Infrastructure: The lack of developed infrastructure in the region can pose challenges for travelers. Adequate planning and preparation, including provisions for food, water, and transportation, are essential.

It’s advisable for individuals interested in visiting the Eye of the Sahara to check for the latest travel advisories, obtain up-to-date information on accessibility, and consider guided tours or organized expeditions for a safer and more informative experience. Additionally, consulting with local authorities and experts on the region is crucial to understanding the current conditions and requirements for visiting this unique geological formation.

Summary of Key Findings

The Eye of the Sahara, also known as the Richat Structure, is a massive circular geological formation located in the Sahara Desert near Ouadane, Mauritania. Key findings and features include:

Formation: The Eye of the Sahara is not an impact crater, as initially hypothesized, but likely formed through a combination of uplift, erosion, and exposure of sedimentary rock layers.
Geological Features: Its circular structure spans approximately 30 miles in diameter, with concentric rings and a raised central peak. The alternating layers of sedimentary rocks provide a record of Earth’s geological history.
Scientific Significance: Researchers have conducted geological studies, employed dating techniques, and used remote sensing technologies to better understand the Eye of the Sahara. The structure serves as a natural laboratory for studying landscape evolution and geological processes.
Cultural and Folklore Significance: While not as pronounced as some other geological formations, the Eye of the Sahara has gained attention in scientific tourism, fostering cultural exchange and local appreciation for its unique features.
Challenges and Future Research: Unanswered questions persist, including the precise mechanism of formation, the chronology of events, and the potential for microbial life. Ongoing and future research is expected to address these questions, contributing to our understanding of Earth’s geological evolution.

Significance in the Field of Geology:

Geological Evolution: The Eye of the Sahara provides valuable insights into the geological evolution of Earth. Its sedimentary rocks offer a chronological record of environmental conditions and geological processes spanning millions of years.
Natural Laboratory: As a unique and well-exposed geological structure, the Eye of the Sahara serves as a natural laboratory for scientists studying terrestrial processes. It aids in understanding the interplay of uplift, erosion, and other geological forces.
Planetary Analogs: Comparative planetary geology studies using the Eye of the Sahara contribute to our understanding of similar features on other planets. It serves as an analog for scientists exploring the landscapes of Mars and other celestial bodies.

Final Thoughts on the Eye of the Sahara: The Eye of the Sahara stands as a captivating and enigmatic geological wonder that challenges our understanding of landscape formation. While its remote location presents challenges for accessibility, the scientific and cultural interest in this structure continues to grow. Ongoing research promises to unravel more of its mysteries, contributing not only to the field of geology but also to our broader understanding of the Earth’s dynamic history and the forces shaping its surface. The Eye of the Sahara remains a testament to the complexity and beauty of our planet’s geological processes.

Great Blue Hole

The Blue Hole in Belize is a natural wonder that has captivated divers and adventurers from all around the world. Located off the coast of Belize, this circular sinkhole is approximately 300 meters wide and 125 meters deep, making it one of the largest and most unique diving destinations on the planet. The Blue Hole is surrounded by crystal-clear waters and an abundance of marine life, including sharks, rays, and colorful fish, making it a must-visit spot for any diving enthusiast. In this article, we’ll explore the history and geology of the Blue Hole, as well as the diverse wildlife that calls it home, and the best ways to experience this awe-inspiring natural wonder for yourself.

The formation of the Blue Hole began during the last ice age, approximately 15,000 years ago when the sea level was much lower than it is today. At that time, the area was a large, limestone cave system that was gradually flooded as the sea level rose. Over time, the roof of the cave system collapsed, creating the circular sinkhole that we see today.

One of the most notable features of the Blue Hole is its deep blue color, which is caused by the depth of the sinkhole and the lack of sunlight penetrating its depths. The walls of the sinkhole are sheer and almost vertical, with an array of fascinating geological formations, including stalactites, stalagmites, and other limestone formations.

The Blue Hole is also home to a diverse range of marine life, including sharks, barracuda, and other tropical fish species. It is a popular destination for scuba divers and snorkelers, who come from all over the world to explore its depths and marvel at its natural beauty.

Overall, the Blue Hole is an extraordinary geological formation that provides a fascinating insight into the natural processes that shape our planet. Its unique features and stunning beauty make it one of the most remarkable natural wonders in the world.

Contents

Geologic features of the Blue Hole
Explanation of how the Blue Hole was formed
Overview of the limestone cave system and its role in the Blue Hole’s formation
Overview of the diving experience in the Blue Hole

Geologic features of the Blue Hole

The Blue Hole is a unique geological formation with a variety of features that make it a wonder of the natural world. Some of its most notable geological features include:

Sinkhole: The Blue Hole is a large, circular sinkhole that measures approximately 300 meters (984 feet) across and 124 meters (407 feet) deep. It is the result of the collapse of a limestone cave system that was flooded by rising sea levels.
Limestone formations: The walls of the Blue Hole are made of limestone, a sedimentary rock that forms from the accumulation of calcium carbonate over millions of years. The limestone walls are home to a variety of geological formations, including stalactites, stalagmites, and other cave formations.
Deep blue color: The Blue Hole gets its name from its deep blue color, which is caused by the depth of the sinkhole and the lack of sunlight that penetrates its depths. The water appears dark blue from the surface and becomes almost black as it gets deeper.
Marine life: The Blue Hole is home to a diverse range of marine life, including sharks, barracuda, and other tropical fish species. The unique underwater environment of the sinkhole creates a habitat for these species that is different from other areas of the ocean.
Ancient fossils: The Blue Hole is also home to a number of ancient fossils, including the remains of extinct species like the giant sloth and the sabre-toothed tiger. These fossils provide valuable insights into the history of the region and the evolution of life on Earth.

Explanation of how the Blue Hole was formed

The formation of the Blue Hole began during the last ice age, approximately 15,000 years ago.

At that time, the sea level was much lower than it is today, and the area was a large, limestone cave system that had formed over millions of years. As the sea level rose, the cave system gradually flooded with seawater. Over time, the weight of the water caused the cave ceiling to collapse, creating a large sinkhole.

The collapse of the ceiling left behind sheer walls of limestone that form the walls of the Blue Hole. The limestone walls are also home to a variety of geological formations, including stalactites, stalagmites, and other cave formations. The deep blue color of the water is caused by the depth of the sinkhole and the lack of sunlight that penetrates its depths.

Overview of the limestone cave system and its role in the Blue Hole’s formation

Limestone is a sedimentary rock that forms over millions of years from the accumulation of calcium carbonate, typically from the shells of marine organisms. Over time, the buildup of limestone can form extensive cave systems underground.

In the case of the Blue Hole, the cave system was likely formed through a combination of geological processes, including the dissolution of limestone by acidic groundwater and the erosion caused by flowing water. As the cave system formed, it created a series of interconnected chambers and tunnels that were eventually filled with water.

During the last ice age, the sea level was much lower than it is today, and the limestone cave system was above sea level. As the sea level gradually rose, seawater flooded the cave system through underground channels, and the weight of the water caused the cave roof to collapse, forming the circular sinkhole that we see today.

The collapse of the cave roof created the sheer walls of limestone that form the walls of the Blue Hole. These walls are also home to a variety of geological formations, including stalactites, stalagmites, and other cave formations.

In conclusion, the limestone cave system played a crucial role in the formation of the Blue Hole. The gradual accumulation of limestone over millions of years created the cave system, and the rising sea levels during the last ice age flooded the system, leading to its eventual collapse and the formation of the Blue Hole. The limestone walls of the Blue Hole are a testament to the natural geological processes that shape our planet over time.

Overview of the diving experience in the Blue Hole

The Blue Hole is a world-renowned diving destination located off the coast of Belize in the Caribbean Sea. The diving experience in the Blue Hole is unlike any other, offering divers the opportunity to explore a unique underwater environment with an abundance of marine life and geological formations.

Diving in the Blue Hole typically involves a descent to depths of up to 40 meters (130 feet) and requires a high level of diving experience and certification. The dive itself can take around 45 minutes, with divers exploring the walls of the sinkhole and descending to the famous stalactites that can be found at around 30 meters (100 feet) deep.

The Blue Hole is known for its crystal-clear water, which offers excellent visibility for divers. The deep blue color of the water is caused by the depth of the sinkhole and the lack of sunlight that penetrates its depths. As divers descend deeper into the Blue Hole, they will be able to see a variety of marine life, including reef sharks, barracuda, and other tropical fish species.

The limestone walls of the Blue Hole are also home to a variety of geological formations, including stalactites and stalagmites. These formations were once above sea level but were submerged when the sea level rose and the cave system collapsed to form the sinkhole. The formations are a testament to the geological processes that shaped the Blue Hole over thousands of years.

Overall, diving in the Blue Hole offers a unique and unforgettable experience for divers. The combination of stunning geological formations, crystal-clear water, and diverse marine life make it one of the most remarkable diving destinations in the world.

Here are ten things you probably didn’t know about the great blue hole of Belize.

The Hole is a tremendous underwater sinkhole that is located off the coast of Belize and lies near the center of Lighthouse Reef.
The actual name of “The Great Blue Hole” was created by British diver and author Ned Middleton after having lived in Belize for 6 months. He was so impressed with this natural feature that he reasoned in his book “Ten Years Underwater” that if Australia could have ‘The Great Barrier Reef’ then Belize could equally have ‘The Great Blue Hole’ thus setting this feature apart from similar, albeit lesser in size, structures.
The hole is circular in shape and has over 300 meters across and 125 meters deep. It is the world’s largest natural formation of its kind and is part of the Belize Barrier Reef System.
Giant stalactites, dripstone sheets, and columns can be found inside the blue hole. Scientists believe that these structures were formed in a dry cavern above sea level during glacial periods.
Analysis of stalactites found in Blue Hole shows that formation took place 153,000; 66,000; 60,000; and 15,000 years ago.
The French Explorer Jacques Cousteau revealed the secrets of the Blue Hole to millions of viewers in a television series called “The Undersea World of Jaques-Cousteau”.
The Blue Hole Monument is one of the seven wonders of Belize’s World Heritage site.
In April of 2012, Bill Gates, the 2^nd richest man in the world visited the Great Blue Hole with his family.
Day trips to the Great Blue Hole are full-day trips and are offered from the coastal tourist communities in Belize. The tour usually includes one dive in the Blue Hole and a dive on Half Moon Wall.
The Discovery Channel ranked the Blue Hole as number one on its list of “The 10 Most Amazing Places on Earth”.

The Earth’s Layers

Contents

What are the major layers of the Earth?
Do geologists subdivide the Earth in any other way
What is the difference between compositional and mechanical layering of the Earth?
Who gave the first scientific explanation of the Earth’s interior?

What are the major layers of the Earth?

The Earth is generally divided into four major layers: the crust, mantle, inner core, and outer core. The following defines each division. (Note: numbers representing the thickness and depth of these layers differ depending on the reference; thus, the numbers here should be taken as approximations):

Crust-The Earth’s crust is the outermost layer and is the most familiar, since people live on the outer skin of the crust. It is rigid, brittle, and thin compared to the mantle, inner core, and outer core. Because of its varying characteristics, this outer layer is divided into the continental and oceanic crusts.

Mantle-In general, the Earth’s mantle lies beneath the crust and above the outer core, averaging about 1,802 miles (2,900 kilometers) thick and repre· senting 68.3 percent of the Earth’s mass. A transition zone divides this layer into the upper and lower mantles.

Outer core-The liquid outer core is a layer between 1,793 and 3,762 miles (2,885 and 5,155 kilometers) deep in the Earth’s interior. It is thought to move by convection (the transfer of heat through the circulating motion of particles-in this case, the material that makes up the outer core), with the movement possibly contributing to the Earth’s magnetic field. The outer core represents about 29.3 percent of the Earth’s total mass.

Inner core-The inner core is thought to be roughly the size of the Earth’s Moon. It lies ata depth of 3,762 to 3,958 miles (5,150 to 6,370 kilometers) beneath the Earth’s surface and generates heat close to temperatures on the sun’s surface. It represents about 1.7 percent of the Earth’s mass and is thought to be composed of a solid iron-nickel alloy suspended within the molten outer core

Do geologists subdivide the Earth in any other way

Yes, geologists have another way of looking at the Earth’s interior layers. The following list refers to this view:

Lithosphere-The lithosphere (Ii/has is Greek for “stone”) averages about 50 miles (80 kilometers) thick and is composed of both the crust and part of the upper mantle. Overall, it is more rigid than deep, yet more molten mantle and cool enough to be tough and elastic. It is thinner under the oceans and in volcanically active continental regions, such as the Cascades in the western United States. The lithosphere is physically broken up into the brittle, moving plates containing the world’s continents and oceans. These lithospheric plates appear to “float” and move around on the more ductile asthenosphere. (For more on plate tectonics, see below).

Asthenosphere-A relatively narrow, moving zone in the upper mantle, the asthenosphere (asthenes is Greek for “weak”) is generally located between 45 to 155 miles (72 to 250 kilometers) beneath the Earth’s surface. It is composed of a hot, semi-solid material that is soft and flowing after being subject- ed to high temperatures and pressures; the material is thought to be chemically similar to the mantle. The asthenosphere boundary is closer to the sur~ face-within a few miles-under oceans and near mid-ocean ridges than it is beneath landmasses. The upper section of the asthenosphere is thought to be the area in which the lithospheric plates move, “carrying” the continental and oceanic plates across our planet. The existence of the asthenosphere was theorized as early as 1926, but it was not confirmed until scientists studied seismic waves from the Chilean earthquake of May 22, 1960.

What is the difference between compositional and mechanical layering of the Earth?

When scientists talk about the Earth’s crust (oceanic or continental), mantle, and cores, they are discussing layers with distinct chemical compositions; thus, it is referred to as compositional layering. The lithosphere and asthenosphere differ in terms of their mechanical properties (for example, the lithosphere moves as a rigid shell while the asthenosphere behaves like a thick, viscous fluid) rather than their composition, so this is why the term mechanical layering applies.

Who gave the first scientific explanation of the Earth’s interior?

Empedocles, a philosopher who lived during the 400s B.O:., was one of the first to formulate a scientific description of the Earth’s interior. He believed the inside of the Earth was composed of a hot liquid. In fact, Empedocles was close to the truth. Modern scientists realize that the Earth’s interior does not hold mythical beings but megatons of rock and molten matter

What was the Precambrian?

Precambrian is the oldest part of the history of the Earth, founded before the present Phanerozoic Eon. It was called the Precambrian, because it came before Cambrian, the first period of Phanerozoic eon after Cambria, the Latin name in Wales where the rocks were studied for the first time. Precambrian constitutes 88% of the geological time in the world.

Most sources list the this as an era; others just refer to it as “Precambrian Time.” In other words, like many other parts of the geologic time scale, there are disagreements among charts.

Most charts do agree that the time of this is broken down into several other divisions. In some countries, it is divided into the following: Hadean (after Hades, with no rock record so far discovered); Archean (meaning ancient-it contains little evidence of life, and the Earth conditions were very dissimilar to today’s planet); and Proterozoic (meaning early life-a time when multicellular organisms started to appear as fossils and conditions on Earth were becoming more similar to today’s). Other charts divide into the Priscoan (oldest), Archean, and Proterozoic, while still other scales mention merely the Archean and Proterozoic.

But there is one thing everyone seems to agree upon so far: The Precambrian included about 80 percent of Earth’s history, lasting from about 4.56 billion years ago to about 545 million years ago. During this time, the most significant Earth events occurred, including the formation of the Earth, the beginnings of life, the first movement of tectonic plates, the formation of eukaryotic cells, and the enrichment of the atmosphere with oxygen. Just before the Precambrian ended, multicellular organisms evolved, including those that eventually produced the first plants and animals.

Age of the Earth and Earth’s Oldest Rock

How old is the Earth?

Thanks to meteorites from space, rocks brought back by the Apollo astronauts from the Moon, and sundry other long-distance readings (mostly from satellites) taken of planetary bodies throughout the solar system, scientists have been able to calculate the age of the Earth. They believe the planets, including the Earth, formed between 4.54 to 4.58 billion years ago. In general, most scientists say that the Earth formed somewhere in between-about 4.55 to 4.56 billion years ago. (For more information about the Earth’s age, see “The Earth in Space.”)

The reason for the reliance on other space bodies to determine the Earth’s age is simple: The movement of the lithospheric plates around our planet has recycled and destroyed the Earth’s oldest rocks. If there are any primordial rocks left on Earth, they have yet to be discovered. Therefore, scientists must use other means to infer the age of our planet, including the absolute dating of planetary rocks that probably formed at the same time as the Earth.

What are some of the oldest rocks so far discovered on Earth?

Scientists have found rocks exceeding 3.5 billion years of age on all the Earth’s continents. But the oldest rocks uncovered so far are the Acasta Gneisses in north-western Canada near Creat Slave Lake, which has been dated at about 4.03 billion years old. Others that are not as old include the lsua Supracrustal rocks in West Greenland (3.7 to 3.8 billion years old), rocks from the Minnesota River Valley and northern Michigan (3.5 to 3.7 billion years old), rocks in Swaziland (3.4 to 3.5 billion years old), and rocks from western Australia (3.4 to 3.6 billion years old). These ancient rocks are mostly from lava flows and shallow water sedimentary processes. This seems to indicate that they were not from the original crust, but formed afterward.

The oldest materials found on Earth to date are tiny, single zircon crystals uncovered in younger sedimentary layers of rock. These crystals, found in western Australia, have been dated at 4.3 billion years old, but the source of the crystals has not yet been discovered.

Field Geology Maps Questions and Answers

Contents

What is a topographic map?
What are contour lines on topographic maps?
What are some of the major rules for contour lines on a map?
What are bathymetric contours?
How do you determine the scale of a topographic map?
What is a geologic map?
How do geologists use strike and dip while in the field?

What is a topographic map?

A topographic map (also called a “tapa” map) is a field map that represents a scale model of part of the Earth’s surface. Using special symbols and lines, it shows the three-dimensional shapes of the surface using two dimensions. Topo maps are used a great deal by geologists in the field, primarily to gather information about features, map certain interesting rock areas, and to generally get around rougher terrain.

What are contour lines on topographic maps?

The most important features on topographic maps are contour lines: the brown lines of differing widths that represent points of equal elevation. These lines symbolize the shape of the Earth’s surface, with each line representing the land as if it were sliced by a horizontal plane at a particular elevation above sea level. Thicker contour lines called index contours-usually shown as every fifth contour line-make it easier for the user to determine elevations. Contour lines that are very close together represent steep slopes, while widely spaced contours or no contours at all-represent relatively level ground. The contour lines also represent a distance called the contour interval, or the difference in elevation represented by adjacent contour lines. Each map has a different contour interval listed on the map’s legend. For example, a relatively flat area may have a contour interval of 10 feet (3 meters) or less, meaning that the difference between each contour line will be 10 feet (3 meters) up or down in elevation; a mountainous area may have a contour interval of 100 feet (30 meters) or more.

What are some of the major rules for contour lines on a map?

There are several major rules contour lines must follow. In particular, contour lines must not cross (except in the rare case of an overhanging cliff); spacing represents either a very steep slope (lines close together) or wide plains (lines wide apart); a hill is represented by a series of closed contour lines “stacked” on one another like a lopsided bull’s eye (depressions are the same, but contain hatch marks within the closed contour lines-or the downhill side); contour lines must never diverge; and when contour lines cross stream or river valleys, they must form Vs that point upstream.

What are bathymetric contours?

Bathymetric contours are similar to regular contours, except they depict the elevations, shape, and slope of marine features offshore (usually the bottom floors of bays, seas, and oceans). These contours are in black or blue, and they are usually written in meters at various intervals, depending on the map scale. They should not be confused with maps that depict depth curves, which usually represent water depths along coast~ lines and inland bodies of water. The contours of these maps are usually show in blue, with the data coming from hydrographic charts and depth soundings.

How do you determine the scale of a topographic map?

A topographic map’s scale-no matter which scale is used-represents the horizontal distances on the map (not elevation distances, which are shown by contour lines). Similar to a street or highway map, the scale can vary widely, depending on the map. But the topographic map’s scale differs in a major way, by allowing the easy interpretation of each map’s distances. Topographic maps are notorious for using different scales, depending on how much detail is desired. Each scale comes with a map ratio. For example, a map with a scale of 1:25,000 means one inch on the map is equal to 25,000 inches on the ground. And because both numbers use the same units, it can also be interpreted as any unit measure. For example, the same map could also be interpreted as 1 centimeter equals 25,000 centimeters on the ground. For those who prefer to measure in miles and kilometers, most topographic maps also offer a graphic scale in the legend.

What is a geologic map?

A geologic map is actually a form of topographic map, but in this case it shows the type of sediment or rock outcrops exposed at the Earth’s surface, along with the contour lines. The information on these maps can range from the rock type and age to the orientation of rock layers and major (and sometimes minor) geologic features. Who uses these maps? Most geologists involved in almost every phase of field geology use geologic maps. For example, petrologists use these maps to determine the location of possible economic resources, such as metal ores, water, or oil. Ceomor· phologists use such maps to detect potential hazards in various areas, such as areas prone to earthquakes, flooding, or landslides. Occasionally, geologic profiles are also provided on these maps to help scientists understand, for example, the rock underlying an area.

How do geologists use strike and dip while in the field?

Strike and dip are not baseball terms; rather, they are used by geologists in the field to determine how rock layers and/or outcrops lean (or don’t lean) in certain directions. Both are very useful to geologists as they map rock outcrops and geologic features. Dip is the angle at which a layer or rock is inclined from the horizontal. It is usually measured with a clinometer. This instrument contains a straightedge that is lined up against the dip of the rock; a weight is used to measure the angle. Strike is the opposite-a line that a dipping rock layer makes with the horizontal (one way of visualizing it is to think how a waterline would form if the rock layer dipped into a lake). Geologists often use a compass to measure strike.

Plagioclase Feldspar

Plagioclase is series of framework silicate minerals in feldspar group. Plagioclase is a continuous series of solid solutions known as the plagioclase feldspar series, rather than a specific mineral with a particular chemical composition. The series ranges from albite to anorthite endmembers (with respective compositions NaAlSi3O8 to CaAl2Si2O8), where sodium and calcium atoms can substitute for each other in the mineral’s crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or ‘record-groove’ effect.

Name: From the Greek plagios – “oblique” and klao – “I cleave” in allusion to the obtuse cleavage angles of the good cleavages.

Polymorphism & Series: Low- and high-temperature structural modi¯cations are recognized.

Mineral Group: Feldspar group, plagioclase series.

Environment: Igneous and metamorphic rocks. Group name for Na, Ca feldspars.

Contents

Plagioclase series members
Feldspar classification
Plagioclase Feldspar Chemical Properties
Plagioclase Feldspar Physical Properties
Albite Optical Properties
Anorthite Optical Properties
Plagioclase Occurrence
Plagioclase Uses Area
Distribution
References

Plagioclase series members

The composition of plagioclase feldspar is typically indicated by the general anorthite (% An) or albite (% Ab) fraction and is easily determined by measuring the refractive index or peel angle within the crushed particles by measuring the refraction angle under a thin section. The deflection angle is an optical characteristic and varies according to the albite fraction (Ab). There are several plagioclase feldspars in the series between albite and anorthite.

Feldspar classification

This diagram shows how feldspar minerals are classified on the basis of their chemical composition. The sequence of minerals along the base of the triangle represents the solid solution series of plagioclase between albite and anorthite

Plagioclase Group Minerals
Mineral	% Albite	% Anorthite
Albite	100-90% Ab	0-10% An
Oligoclase	90-70% Ab	10-30% An
Andesine	70-50% Ab	30-50% An
Labradorite	50-30% Ab	50-70% An
Bytownite	30-10% Ab	70-90% An
Anorthite	10-0% Ab	90-100% An

Plagioclase Feldspar Chemical Properties

Chemical Classification	Silicate
Chemical Composition	NaAlSi3O8 – CaAl2Si2O8

Plagioclase Feldspar Physical Properties

Color	Usually white or gray. Also colorless, yellow, orange, pink, red, brown, black, blue, green.
Streak	White
Luster	Vitreous. Pearly on some cleavage faces.
Cleavage	Perfect in two directions that intersect at approximately 90 degrees.
Diaphaneity	Translucent to transparent
Mohs Hardness	6 to 6.5
Crystal System	Triclinic
Tenacity	Brittle
Specific Gravity	2.6 to 2.8

Plagioclase Mineral under the microscope

Albite Optical Properties

Color / Pleochroism	White to gray, bluish, greenish, Reddish; may be chatoyant.
2V:	Measured: 45° , Calculated: 76° to 82°
RI values:	nα = 1.528 – 1.533 nβ = 1.532 – 1.537 nγ = 1.538 – 1.542
Optic Sign	Biaxial (+)
Birefringence	δ = 0.010
Relief	Low
Dispersion:	Low

Anorthite Optical Properties

Color / Pleochroism	White, grayish, reddish; colorless in thin section
2V:	Measured: 78° to 83°, Calculated: 78°
RI values:	nα = 1.573 – 1.577 nβ = 1.580 – 1.585 nγ = 1.585 – 1.590
Optic Sign	Biaxial (-)
Birefringence	δ = 0.012 – 0.013
Relief	Moderate
Dispersion:	r < v weak

Plagioclase Occurrence

Plagioclase feldspar group minerals are the most common rock-forming minerals. They are importantly dominant minerals in most igneous rock. They are major constituents in a wide range of intrusive and extrusive igneous rocks including granite, diorite, gabbro, rhyolite, andesite, and basalt. Plagioclase minerals are important constituents of many metamorphic rocks, such as gneiss, where they can be inherited from an igneous protolith or formed during the regional metamorphism of sedimentary rocks.

Plagioclase is a common clast produced during the weathering of igneous and metamorphic rocks. It can be the most abundant clast in sediments located close to their source area and decreases in abundance downstream. This decrease is partly because quartz is more physically and chemically durable than feldspar and persists in greater relative quantities downstream in eroded sediments.

Plagioclase Uses Area

Plagioclase minerals are important constituents of some building stone and crushed stone such as granite and trap rock.
Some rare specimens of plagioclase exhibit optical phenomena that make them highly desirable gem materials.
Moonstone is a name given to a gem material that consists of very thin, alternating layers of orthoclase (an alkali feldspar) and albite (a plagioclase feldspar).
Some specimens of labradorite exhibit a schiller effect, which is a strong play of iridescent blue, green, red, orange, and yellow colors when moved under a source of incident light.

Distribution

Anorthite

A widely distributed rock-forming mineral. Classic occurrences include:

from Monte Somma and Vesuvius, Campania; on Mt. Monzoni, Val di Fassa, Trentino-Alto Adige; and from the Cyclopean Islands, Italy.
At Tunaberg, SÄodermanland, Sweden. From near Lojo, Finland.
At Bogoslovsk and Barsowka, Ural Mountains, Russia.
On Miyakejima Island, Tokyo Prefecture; at Toshinyama, Tochigi Prefecture; the Zao volcano, Yamagata Prefecture; Otaru, Hokkaido; and other places in Japan.
In the USA, on Great Sitkin Island, Aleutian Islands, Alaska; from Grass Valley, Nevada Co., California.
On Amitok Island, Labrador, Newfoundland, Canada.

Albite

Widespread; a few localities for good crystals are:

In Switzerland, from St. Gotthard, Ticino and Tavetsch, GraubuÄnden. From Roc Tourne, near Modane, Savoie, France.
On Mt. Greiner, Zillertal, Tirol, Austria.
At Baveno, Piedmont, and in the P¯tschtal, Trentino-Alto Adige, Italy.
From Mursinka, Ural Mountains, and Miass, Ilmen Mountains, Southern Ural Mountains, Russia.
In the USA, at Haddam and Middletown, Middlesex Co., Connecticut; Amelia, Amelia Co., Virginia; from Diana, Lewis Co., and Dekalb, Macomb, and Pierrepont, St. Lawrence Co., New York. On Prince of Wales Island, Alaska; in the Pala and Mesa Grande districts, San Diego Co., California.
At Bathurst, and Wicklow Township, Hastings Co., Ontario, Canada.
From Virgem da Lapa and Morro Velho, Minas Gerais, Brazil.

References

Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
Mindat.org. (2019). Orpiment: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
Smith.edu. (2019). Geosciences | Smith College. [online] Available at: https://www.smith.edu/academics/geosciences [Accessed 15 Mar. 2019].

Why is the world so cold when it’s closest to the sun in January?

This is definitely a question that would be asked by someone in the Northern Hemisphere, since January in the Southern Hemisphere is definitely warm! From a global perspective, when the Earth is farther away from the sun in its orbit, the average temperature does increase by about 4°Fahrenheit (2.3°Celsius), even though the sunlight falling on Earth at aphelion is about 7 percent less intense than at perihelion.

So why is it warmer when we are farther away from OUf star? The main reason is the uneven distribution of the continents and oceans around the globe. The Northern Hemisphere contains more land, while the Southern Hemisphere has more ocean. During July (at aphelion), the northern half of our planet tilts toward the sun, heating up the land, which warms up easier than the oceans. During January, it’s harder for the sun to heat the oceans, resulting in cooler average global temperatures, even though the Earth is closer to the sun.

But there is another cause for warm temperatures in the north when the Earth is at aphelion: the duration of summers in the two hemispheres. According to Kepler’s second law, planets move more slowly at aphelion than they do at perihelion. Thus, the Northern Hemisphere’s summer is 2 to 3 days longer than the Southern Hemisphere’s summer, giving the sun more time to bake the northern continents.

Who are the famous geologists in history?

Geology is a science of earth. There are many geoscientists from past to present. These people have made great contributions to today’s modern geology.

Contents

Georgius Agricola
Nicolaus Steno
Abraham Gottlob Werner
What was James Hutton’s contribution to geology?
John Playfair
James Hall
Louis Agassiz
What was James Dwight Dana’s contribution to geology?
Clarence Edward Dutton?
Grove Karl Gilbert
Thomas Chrowder Chamberlin
Matthew Fontaine Maury
Vasily Vasilievich Dokuchaev
John Wesley Powell
Robert Elmer Horton
Who is considered the greatest petrologist of the 20th century?
William Morris Davis
Beno Gutenberg
Preston Cloud

Georgius Agricola

Georgius Agricola (Georg Bauer, 1494-1555) was a German scientist who is also thought of by many as the “father of mineralogy.” Agricola was originally a philologist (a person who studies ancient texts and languages); later, he worked in the greatest mining region of Europe of that time, near Joachimsthal, Germany. As a result of this experience, he produced seven books on geology that set the stage for the development of modern geology two centuries later. His main contributions were compiling all that was known about mining and smelting during his time and suggesting ways to classify minerals based on their observable properties, such as hardness and color

Nicolaus Steno

Nicolaus Steno (Niels Stensen; 1638-1686) was a Danish geologist and anatomist. In 1669, he determined that the so-called “tonguestones” sold on the Mediterranean island of Malta as good luck charms were actually fossilized sharks’ teeth. He also developed what is cal1ed Steno’s law, or the principle ofsuperposition. This theory says 4 that in any given rock layer, the bottom rocks are formed first and are the oldest. Steno proposed two other principles: that rock layers are initially formed horizontally (often called the law of original horizonality), and that every rock outcrop in which only the edges are exposed can be explained by some process, such as erosion or earthquakes (often called the law of concealed stratification), All of these principles are generally held to be true today. Some people consider Steno to be the “father of modern geology,” a title also given to several other early geologists, including James Hutton.

Abraham Gottlob Werner

Abraham Gottlob Werner (1750-1817) was a German geologist and mineralogist who first classified minerals systematically based on their external characteristics. He also was a great believer in neptunism.

What was James Hutton’s contribution to geology?

James Hutton (1726-1797) was a Scottish natural philosopher, but his contribution to geology was even more important: He is considered by some to be the “father of modern geology.” Hutton was also an avid follower of plutonism and the author of Theory ofthe Earth, a book that emphasized several fundamentals of geology, including that the Earth was older than 6,000 years, that subterranean heat creating metamorphic material is just as important a process as rock forming from sediments laid down underwater, and that the exact same agents that are operating today created the landforms of the past, a principle also known as uniformitarianism.

John Playfair

Scottish geologist John Playfair (1748-1819) went against most of his contemporaries in proposing that river valleys were actually carved by streams, an idea that is readily accepted today. Many of his peers believed that valleys formed during cataclysmic upheavals of the land, with the rivers flowing through much later

James Hall

Scottish geologist Sir James Hall (1761- 1832) was one of the first to establish experimental research as an aid in geological investigations. For example, one of his experiments demonstrated how lava forms different kinds of rocks as it cools. Hall was also friends with James Hutton and John Playfair; his rock studies helped confirm many of Hutton’s views regarding intrusive rock formations.

Louis Agassiz

Jean Louis Rodolphe Agassiz (1807-1873), best known simply as Louis Agassiz, was the Swiss-born geologist and paleontologist who introduced the concept of the ice ages, periods of time when glaciers and ice sheets covered much of the Northern Hemisphere. Agassiz announced this astonishing idea in a famous speech to the Swiss Society of Natural Sciences in 1837. “lee ages” was a term he adopted from Karl Schimper (1803-1867), who coined the phrase the year before. Agassiz later moved to the United States, where he was a dominant force in the fields of geology and paleontology until his death. Interestingly, he was one of many scientists who rejected his contemporary Charles Darwin’s theory of natural selection.

What was James Dwight Dana’s contribution to geology?

James Dwight Dana (1813-1895) was an American mineralogist who compiled a book that is still one of the most respected works in mineralogy: Dana’s Manual ofMineralogy. First published in 1862, the book was only one of Dana’s to become a standard reference book in geology. It covers most of the known minerals and metals on Earth and includes their chemical formulas, characteristics, uses, and sundry other useful information.

Clarence Edward Dutton?

Clarence Edward Dutton (1841-1912) was a American geologist who, among other geologic ventures, pioneered the theory of isostasy, which describes how land can rise up as a result of events such as retreating glacial ice sheets. He also worked on a Tertiary history of the Grand Canyon, Arizona, detailing the rock layers of that period in the region in his classic book, Tertiary History orthe Grand Canyon District (1882).

Grove Karl Gilbert

Grove Karl Gilbert (1843-1918)-no known relation to William Gilbert-was an American geologist and geomorphologist who laid the foundations for much of the 20th-century’s advances in geology. His monographs, including The Transportation of Debris by Running Water (1914), greatly contributed to theories of river development. He was also known for making other contributions, such as to theories about glaciation and the formation of lunar craters, as well as to the philosophy of science.

Thomas Chrowder Chamberlin

Thomas Chrowder Chamberlin (1843-1928) was an American geologist whose primary interest was in glacial geology, and he was a proponent of the idea of multiple glaciations. He also established the origin of loess (wind-blown deposits of silt); discovered fossils in 8 Greenland, suggesting that the landmass had experienced an earlier, warmer climate; and developed theories on the Earth’s origin (Chamberlin proposed the planetesimal origin of our planet, going against the more commonly accepted nebula-gascloud theory), fonnation, and growth.

Matthew Fontaine Maury

Matthew Fontaine Maury (1806-1873) was an American oceanographer who wrote the first text on modern oceanography, Physical Geography ofthe Sea and its Meteorology (1855). He also provided guides for ocean currents and trade winds-compiled from ships’ logswhich helped cut sailing time for ships on many routes.

Vasily Vasilievich Dokuchaev

Vasily Vasilievich Dokuchaev (1846-1903; also seen as Vasily Vasilyevich Dokuchaev) was a Hussian geographer who is considered by many scientists to be the founder of modern soil science. He reasoned that soils form by the interaction of climate, vegetation, parent material, and topography over a certain amount of time. He also suggested that soils form zones, but the idea of zonal soils would not be fully developed until later.

John Wesley Powell

John Wesley Powell (1834-1902) was an American geologist, soldier, and administrator who, despite losing an arm in the Civil War, led the first successful expedition into the Grand Canyon. He described the Colorado canyons and led the United States Geological Survey for a time.

Robert Elmer Horton

Hobert Elmer Horton (1875-1945) was an American engineer, hydrologist, and geomorphologist who was one of the first to develop a qualitative way to describe land forms. He also studied the phenomenon of overland flow of rainwater runoff, a process that was named after him (Horton overland flow).

Who is considered the greatest petrologist of the 20th century?

Many scientists consider the greatest petrologist of the 20th century to be Norman Levi Bowen (1887-1956). He developed the idea of phase diagrams of common rock forming minerals-the Bowen’s reaction series is named after him-thus providing scientists with information about how to interpret certain rock formations.

William Morris Davis

William Morris Davis (1859-1934), an American geologist, geographer, and meteorologist, was an authority on landforms. His articles on the subject advanced the field of geomorphology more than anyone in his time. His most influential concept was the “cycle of erosion” theories, an indication that Davis was greatly influenced by Charles Darwin’s organic evolution theory. In a 1883 paper Davis stated that “it seems most probable, that the many pre-existent streams in each river basin concentrated their water in a single channel of overflow, and that this one channel sUlVives-a fine example of natural selection.

” Because of his studies and theories, he is often called the “founder of geomorphology” and the “father of geography” (some scientists consider both subjects to be very similar, if not the same). He also founded the National Geographic Society.

Beno Gutenberg

Beno Gutenberg (1889-1960) was the foremost observational seismologist of the 20th century. He analyzed seismic records, contributing important discoveries of the structu(e of our solid Earth and its atmosphere. He also discovered the precise location of the Earth’s core and identified its elastic properties. Besides a plethora of other major contributions to seismology, Gutenberg discovered the layer between the mantle and outer core, a division that is now named after him. (For more information about the Earth’s layers, see “The Earth’s Layers.”)

Preston Cloud

Preston Ercelle Cloud Jr. (1912-1991) was a biogeologist, paleontologist, and humanist who left a diverse legacy that cuts across many scientific and other disciplines. A5 an historical geologist, he contributed to our understanding of the atmosphere’s evo~ lution, oceans, and Earth’s crust; he also added to the understanding of the evolution of life. In addition, he was concerned about how humans would continue to evolve in this environment, noting problems with population increases and related activities (for example, pollution) that could greatly affect our planet.

1...868788...98 Page 87 of 98