The single known source in the United States, in Arkansas, has no commercial importance; nor is India, once a source of fine diamonds, a significant present-day supplier.The primary source of diamonds is a soft bluish peridotic rock called kimberlite (after the famous deposit at Kimberley, South Africa), found in volcanic structures called pipes, but many diamonds occur in alluvial deposits presumably resulting from the weathering of primary sources.
Graphite, on the other hand, is a soft slippery solid that is a good conductor of both heat and electricity.
Carbon as diamond is the most expensive and brilliant of all the natural gemstones and the hardest of the naturally occurring abrasives. In microcrystalline and nearly amorphous form, it is used as a black pigment, as an adsorbent, as a fuel, as a filler for rubber, and, mixed with clay, as the “lead” of pencils.
In 1961 the isotope On a weight basis, carbon is 19th in order of elemental abundance in Earth’s crust, and there are estimated to be 3.5 times as many carbon atoms as silicon atoms in the universe.
Only hydrogen, helium, oxygen, neon, and nitrogen are atomically more abundant in the cosmos than carbon.
Coal and coke, for example, are used extensively as fuels.
Charcoal is used as an absorptive and filtering agent and as a fuel and was once widely used as an ingredient in gunpowder.It was later found to occur naturally in tiny amounts on Earth and in meteorites., “to write,” reflects its property of leaving a dark mark when rubbed on a surface.Carbon is the cosmic product of the “burning” of helium, in which three helium nuclei, atomic number 4, fuse to produce a carbon nucleus, atomic number 12.In the crust of Earth, elemental carbon is a minor component.However, carbon compounds (i.e., carbonates of magnesium and calcium) form common minerals (e.g., magnesite, dolomite, marble, or limestone).