Carbon (C)

Where Found

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.

Primary Uses

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.

Technical Definition

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.

Description, Distribution, and Forms

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 oxygen, so that they were not oxidized. Petroleum forms with gradual burial of the animals in the sediment to depths of around 4 to 6 kilometers below the surface at temperatures that range from about 60° Celsius up to 200° Celsius. At temperatures much above 200° the organic constituents in petroleum decompose to natural gas (mostly methane). If the petroleum and methane collect in certain geologic traps, then drilling can potentially extract much of the two substances. Saudi Arabia, Russia, the United States, Iran, China, Mexico, and Canada, in descending order, are the leading producers of petroleum products.

History

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.

Though carbon is one of the major elements that make up the mass of the human body, it makes up a relatively small elemental percentage of the earth's crust. At the same time, it is one of the top-ten most abundant elements found in the universe.

Obtaining Carbon

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 to find such sedimentary structures so that drilling can penetrate the structures to see if petroleum or natural gas is present. Only a small percentage of wells actually tap into petroleum or gas.

Uses of Carbon

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 strong, so they may have applications in products like bulletproof vests.

The radioactive isotope carbon 14 has a half-life of 5,730 years. The atmosphere has a constant supply of carbon 14 that is taken up by growing organisms. If the organisms die, the isotope gradually decays. Thus, that material associated with an archaeological site may be dated based on the remaining carbon 14.

Bibliography

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Labett, Sonia, and Rodney R. White. Carbon Finance: The Financial Implications of Climate Change. John Wiley and Sons, 2007.

Pappas, Stephanie. "Facts about Carbon." Live Science, 9 Aug. 2014, www.livescience.com/28698-facts-about-carbon.html. Accessed 9 Feb. 2017.

Roston, Eric. The Carbon Age: How Life’s Core Element Has Become Civilization’s Greatest Threat. Walker, 2008.

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WebElements. Carbon: The Essentials.http://www.webelements.com/carbon/