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.

Gold Associate Minerals

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

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. 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.
14. 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.
15. 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

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:

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

1. 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.
2. 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.
3. 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.
4. 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.
5. 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:

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

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:

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

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

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

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