Diamond is one of the two best known forms (or allotropes) of
carbon, whose hardness and high dispersion of light make it
useful for industrial applications and jewelry (the other
equally well known allotrope is graphite). 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 USD $9 billion.
The name "diamond" derives from the ancient Greek adamas (αδάμας;
"invincible"). 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. Although nearly four times the mass of natural diamonds are
produced as synthetic diamond each year, the vast majority of
synthetic diamond production remains small, imperfect diamonds
suitable only for industrial-grade use, with gem-quality
synthetic diamonds only recently becoming available.
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.
Diamond is a transparent crystal of pure carbon consisting of
tetrahedrally bonded carbon atoms. Humans have been able to
adapt diamonds for many uses because of the material's
exceptional physical characteristics. Most notable among these
properties are the extreme hardness of diamond, its high
dispersion index, and high thermal conductivity. These
properties form the basis for most modern applications of
diamond.
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