CURRENTLY VIEWING: Diamond
 Diamond is one of the two best known forms (or allotropes) of carbon, whose hardness and high dispersion of light makes it useful for industrial applications and jewelery. The other equally well known allotrope is graphite;but diamonds are specifically renowned as a mineral with superlative physical qualities. They make excellent abrasives because they can only be scratched by other diamonds, which also means they hold a polish extremely well and retain luster. About 130 million carats (26,000 kg) are mined annually, with a total value of nearly 9 billion US$.
The name "diamond" derives from the ancient Greek adamas (??????; "impossible to tame"). They have been treasured as gems since their use as religious icons in India at least 2,500 years ago—and usage in drill bits and engraving tools also dates to early human history. Popularity of diamonds has risen since the 19th century because of improved cutting and polishing techniques, and they are commonly judged by the "four Cs": carat, clarity, color, and cut. Nearly four times the mass of natural diamonds are produced as synthetic diamond each year, though these are typically classified with poor-quality specimens that are suitable only for industrial-grade use.
Most natural diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, Russia, Brazil, and Australia. They are generally mined from volcanic pipes, which are deep in the Earth where the high pressure and temperature enables the formation of the crystals. The mining and distribution of natural diamonds are subjects of frequent controversy—such as with concerns over the sale of conflict diamonds by African paramilitary groups. There are also allegations that the De Beers Group misuses its dominance in the industry to control supply and manipulate price via monopolistic practices.
Diamonds occur in a variety of transparent hues — colorless, white, steel, blue, yellow, orange, red, green, pink, brown—or colored black. Diamonds with a detectable hue to them are known as colored diamonds. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice. The most common impurity, nitrogen, causes a yellowish or brownish tinge.
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