Where Found (Encyclopedia of Global Resources)
Diamond, graphite, and amorphous carbon (charcoal and soot) are the main minerals containing carbon only. Diamond formed in igneous rocks that formed at very great depths in the Earth; graphite formed in some metamorphic rocks. Petroleum, natural gas, and coal are composed of hydrocarbon compounds that formed from plants or animals during burial in sediment.
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Primary Uses (Encyclopedia of Global Resources)
Diamond is used as a gem or as an abrasive. Graphite is mixed with clays to make pencils and is used as a lubricant. petroleum products, natural gas, and coal can be burned to provide heat or to drive engines. Plants and animals are composed of a vast number of hydrocarbon compounds. There are a large number of compounds that have special properties such as silicon carbides that are harder than diamond.
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Technical Definition (Encyclopedia of Global Resources)
Carbon has an atomic number of 6, and it has three isotopes. The isotope C12 composes 99 percent of natural carbon, and C13 makes up about 1 percent of natural carbon. The isotope C14 is radioactive, and it constitutes only a tiny amount of natural carbon. Diamond has a hardness (resistance to scratching by another mineral) of ten, which makes it the hardest of all minerals; graphite has a hardness of two, which makes it one of the softest of all minerals. The density of diamond is 3.52 grams per milliliter, and the density of graphite is 2.27 grams per milliliter. The melting points and boiling points for graphite are high, 3,527° Celsius and 4,027° Celsius, respectively. Diamond does not conduct electricity; graphite does. Diamond is often transparent and colorless, but graphite is opaque and often dark gray. Carbon atoms combine with other atoms of carbon and with hydrogen, sulfur, nitrogen, or oxygen to form the vast number of hydrocarbon compounds found in plants and animals.
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Description, Distribution, and Forms (Encyclopedia of Global Resources)
Graphite has been found in metamorphic rocks that have been raised to moderately high temperatures and pressures so that any of the original hydrocarbon compounds present were destroyed. Graphite has been mined in Greenland, Mexico, Russia, and the United States (New York). Diamond has been found in igneous rocks such as kimberlite and lamproite that have been formed at high pressure in the upper mantle of the Earth and in sediment formed by weathering of the diamond-bearing igneous rocks. Abundant diamonds have been found in South Africa, northern Russia, Australia, Canada, and Botswana. Some graphite and diamonds have been produced artificially.
Plants in forests may be buried out of contact with the Earth’s atmosphere so that they are not oxidized. Thus, with gradually increased burial with other sediment they form peat, lignite coal, bituminous coal, and anthracite coal at gradually higher temperatures, respectively. Peat has lots of volatiles, such as water, so it does not burn well. With increasing burial the volatiles are removed and the carbon content gradually increases. Therefore, anthracite coal burns with a clear, hot flame. Coal is found worldwide. The leading coal producers are the United States, Russia, China, India, Australia, and South Africa.
Petroleum and natural gas form from small animals, such as zooplankton and algae, that have settled out of water, in muds without much...
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History (Encyclopedia of Global Resources)
The word “carbon” was derived from the Latin word meaning charcoal. Diamonds and charcoal have been known for thousands of years. In the eighteenth century, impure iron was changed to steel by using carbon. During that century, charcoal, diamond, and graphite were shown to be the same substance, and some people listed carbon as an elemental substance.
In the early nineteenth century, Michael Faraday and Sir Humphry Davy showed that electricity and chemical changes were linked. Jöns Jacob Berzelius used symbols, like C for carbon, for elemental materials, and he classified elements based on their chemical properties. Faraday lectured on how a candle worked by burning carbon from a candle with air to form “carbonic acid.” He related the carbonic acid (now know to be carbon dioxide) to the gas that animals gave off to the atmosphere.
Later in the nineteenth century, Svante August Arrhenius determined the carbonic acid content of the atmosphere, and he related the carbonic acid content of the atmosphere to the temperature. Also in the nineteenth century, the atomic theory began to be more precisely developed by John Dalton, which led to a better explanation of chemical reactions. Dmitry Ivanovich Mendeleyev organized the known elements into theperiodic table, in which the elements with similar chemical properties were ordered into columns. Thus, he put carbon and silicon in the same columns.
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Obtaining Carbon (Encyclopedia of Global Resources)
Diamonds exist in such low concentrations in igneous rock ores that the ore must first be crushed so that the diamonds are not destroyed. Then, density separations are made to form a diamond-rich fraction, and certain instruments are used to confirm the location of this fraction. Grease belts have been used in the past to concentrate the diamonds, because diamonds stick to the grease. Finally, people carefully look through the diamond-rich fractions to pick out any missed diamonds.
Metamorphic rocks containing graphite are also usually first crushed by grinders. Graphite is less dense than most of the other minerals in the rock, so it is concentrated by floating it to the top of liquids with the right density.
Coal forms in layers in sedimentary rocks. Thus, if the coal is at or close to the surface, the top layers of sediment not containing coal may be stripped off (this procedure is used in Wyoming). The coal is broken up by large pieces of equipment like power shovels, and it is carried off in large vehicles. Underground mines are much more expensive to operate as shafts must be drilled into the coal layer and supports must be installed to keep the open spaces from collapsing.
Petroleum forms in some mudstones, and it must migrate into permeable beds like sandstones. The petroleum has to move into geologic traps, such as at the top of upward folded sedimentary structures like anticlines. Geologists attempt...
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Uses of Carbon (Encyclopedia of Global Resources)
Carbon has a vast number of uses both as an element and in compounds. Diamond can be cut in various ways to make jewelry. Those that are not of jewelry quality, such as artificial diamonds, can be used as abrasives. Powdered graphite is used as a lubricant and, mixed with clays, in pencils.
Coke is a form of carbon that can be burned with a very hot flame to reduce iron ores into iron. Some carbon may be added to the iron to produce carbon steel. Wood, coal, petroleum, and natural gas may be burned as fuels to produce heat or drive engines. Petroleum, for instance, may be refined into gasoline or kerosene.
Carbon compounds compose all living tissue, so they are essential for life. Plant and animal products like cotton, linen, wool, and silk are composed of hydrocarbons. Carbon dioxide is given off to the atmosphere by animals; plants remove the carbon dioxide. Petroleum may be refined to produce plastics.
Charcoal and carbon black are used in oil paint, in watercolors, and in toners for lasers. Activated charcoal is used in gas masks and in water filters to remove poisons. Carbon has been combined with silicon to produce silicon carbides that are harder than diamond.
Fullerenes consist of groups of carbon atoms arranged in hexagonal and pentagonal forms as spheres or cylinders. The spheres can trap other elements within them, and some are superconductors. Some of the fullerene cylinders are exceptionally...
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Further Reading (Encyclopedia of Global Resources)
Homer-Dixon, Thomas, and Nick Garrison. Carbon Shift: How the Twin Crises of Oil Depletion and Climate Change Will Define the Future. Toronto: Random House, 2009.
Janse, A. J. A. “Global Rough Diamond Production Since 1870.” Gems and Gemology 43, no. 2 (2007): 98-119.
Labett, Sonia, and Rodney R. White. Carbon Finance: The Financial Implications of Climate Change. New York: John Wiley and Sons, 2007.
Roston, Eric. The Carbon Age: How Life’s Core Element Has Become Civilization’s Greatest Threat. New York: Walker, 2008.
Saito, R., G. Dresselhaus, and Mildred Dresselhaus. Physical Properties of Carbon Nanotubes. London: Imperial College Press, 1999.
WebElements. Carbon: The Essentials.http://www.webelements.com/carbon/
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Carbon (Chemical Elements)
Carbon is an extraordinary element. It occurs in more different forms than any other element in the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. More than ten million compounds of carbon are known. No other element, except for hydrogen, occurs in even a fraction of that number of compounds.
As an element, carbon occurs in a striking variety of forms. Coal, soot, and diamonds are all nearly pure forms of carbon. Carbon also occurs in a form, discovered only recently, known as fullerenes or buckyballs. Buckyball carbon holds the promise for opening a whole new field of chemistry (see accompanying sidebar).
Carbon occurs extensively in all living organisms as proteins, fats, carbohydrates (sugars and starches), and nucleic acids.
Carbon is such an important element that an entirely separate...
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Carbon (World of Earth Science)
Carbon is the non-metallic chemical element of atomic number 6 in Group 14 of the periodic table, symbol C, atomic weight 12.01, specific gravity as graphite 2.25, as diamond 3.51. Its stable isotopes are 12C (98.90%) and 13C (1.10%). The weight of the 12C atom is the international standard on which atomic weights are based. It is defined as weighing exactly 12.00000 atomic mass units.
Carbon has been known since prehistoric times. It gets its name from carbo, the Latin word for charcoal, which is almost pure carbon. In various forms, carbon is found not only on Earth, but in the atmospheres of other planets, in the Sun and stars, in comets and in some meteorites.
On Earth, carbon can be considered the most important of all the chemical elements, because it is the essential element in practically all of the chemical compounds in living things. Carbon compounds are what make the processes of life work. Beyond Earth, carbon-atom nuclei are an essential part of the nuclear fusion reactions that produce the energy of the Sun and of many other stars. Without carbon, the Sun would be cold and dark.
In the form of chemical compounds, carbon is distributed throughout the world as carbon dioxide gas, CO2, in the atmosphere and dissolved in all the rivers, lakes and oceans. In the form of carbonates, mostly calcium carbonate (CaCO3), it occurs as huge rocky masses of limestone, marble and chalk. In the form of hydrocarbons, it occurs as great deposits of natural gas, petroleum and coal. Coal is important not only as a fuel, but because it is the source of the carbon that is dissolved in molten iron to make steel.
All plants and animals on Earth contain a substantial proportion of carbon. After hydrogen and oxygen, carbon is the most abundant element in the human body, making up 10.7% of all the body's atoms. Carbon is found as the free (uncombined) element in three different allotropic forms-different geometrical arrangements of the atoms in the solid. The two crystalline forms (forms containing very definite atomic arrangements) are graphite and diamond. Graphite is one of the softest known materials, while diamond is one of the hardest.
There is also a shapeless, or amorphous, form of carbon in which the atoms have no particular geometric arrangement. Carbon black, a form of amorphous carbon obtained from smoky flames, is used to make rubber tires and inks black. Charcoalood or other plant material that has been heated in the absence of enough air to actually burns mostly amorphous carbon, but it retains some of the microscopic structure of the plant cells in the wood from which it was made. Activated charcoal is charcoal that has been steam-purified of all the gummy wood-decomposition products, leaving porous grains of pure carbon that have an enormous microscopic surface area. It is estimated that one cubic inch of activated charcoal contains 200,000 ft2 (18,580 m2) of microscopic surface. This huge surface has a stickiness, called adsorption, for molecules of gases and solids; activated charcoal is therefore used to remove impurities from water and air, such as in home water purifiers and in gas masks.
Graphite is a soft, shiny, dark gray or black, greasy-feeling mineral that is found in large masses throughout the world, including the United States, Brazil, England, western Europe, Siberia, and Sri Lanka. It is a good conductor of electricity and resists temperatures up to about 6,332°F (3,500°C), which makes it useful as brushes (conductors that slide along rotating parts) in electric motors and generators, and as electrodes in high-temperature electrolysiscells. Because of its slipperiness, it is used as a lubricant. For example, powdered graphite is used to lubricate locks, where oil might be too viscous. The "lead" in pencils is actually a mixture of graphite, clay, and wax. It is called "lead" because the metallic element lead (Pb) leaves gray marks on paper and was used for writing in ancient times. When graphite-based pencils came into use, they were called "lead pencils."
The reason for graphite's slipperiness is its unusual crystalline structure. It consists of a stack of one-atom-thick sheets of carbon atoms, bonded tightly together into a hexagonal pattern in each sheet, but with only very weak attractionsuch weaker than actual chemical bondsolding the sheets together. The sheets of carbon atoms can therefore slide easily over one another; graphite is slippery in the same way as layers of wet leaves on a sidewalk.
Diamond, the other crystalline form of pure carbon, is the world's hardest natural material, and is used in industry as an abrasive and in drill tips for drilling through rock in oil fields and human teeth in dentists' offices. On a hardness scale of one to ten, which mineralogists refer to as the Mohs scale of hardness, diamond is awarded a perfect ten. But that's not why diamonds are so expensive. They are the most expensive of all gems, and are kept that way by supply and demand. The supply is largely controlled by the De Beers Consolidated Mines, Inc. in South Africa, where most of the world's diamonds are mined, and the demand is kept high by the importance that is widely attributed to diamonds.
A diamond can be considered to be a single huge molecule consisting of nothing but carbon atoms that are strongly bonded to each other by covalent bonds, just as in other molecules. A one-carat diamond "molecule" contains 1022carbon atoms.
The beauty of gem-quality diamonds comes from their crystal clarity, their high refractivity (ability to bend light rays) and their high dispersionheir ability to spread light of different colors apart, which makes the diamond's rainbow "fire." Skillful chipping of the gems into facets (flat faces) at carefully calculated angles makes the most of their sparkle. Even though diamonds are hard, meaning that they can't be scratched by other materials, they are brittlehey can be cracked.
Carbon is unique among the elements because its atoms can form an endless variety of molecules with an endless variety of sizes, shapes and chemical properties. No other element can do that to anywhere near the degree that carbon can. In the evolution of life on Earth, nature has always been able to "find" just the right carbon compound out of the millions available, to serve just about any required function in the complicated chemistry of living things.
Carbon-containing compounds are called organic compounds, and the study of their properties and reactions is called organic chemistry. The name organic was originally given to those substances that are found in living organismslants and animals. Almost all of the chemical substances in living things are carbon compounds (water and minerals are the obvious exceptions), and the name organic was eventually applied to the chemistry of all carbon compounds, regardless of where they come from.
Having the atomic number six, every carbon atom has a total of six protons. Therefore, all carbon atoms with a neutral charge also have a total of six electrons. Two are in a completed inner orbit, while the other four are valence electronsouter electrons that are available for forming bonds with other atoms. An ion is an atom with either a negative or positive charge has either less or more electrons than the number of protons (respectively), and is referred to as either an anion (negatively charged) or a cation (positively charged).
It is impossible to summarize the properties of carbon's millions of compounds. Organic compounds can be classified into families that have similar properties, because they have certain groupings of atoms in common.
See also Carbon dating; Chemical bonds and physical properties; Chemical elements; Gemstones; Geochemistry; Historical geology