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Saturday, February 21, 2009

A scattering of round-brilliant cut diamonds shows off the many reflecting facets.
Category Native Minerals
Chemical formula C
Molecular Weight 12.01 u
Color Typically yellow, brown or gray to colorless. Less often in blue, green, black, translucent white, pink, violet, orange, purple and red.[1]
Crystal habit Octahedral
Crystal system Isometric-Hexoctahedral (Cubic)
Cleavage 111 (perfect in four directions)
Fracture Conchoidal (shell-like)
Mohs Scale hardness 10[1]
Luster Adamantine[1]
Polish luster Adamantine[1]
Refractive index 2.4175–2.4178
Optical Properties Singly Refractive[1]
Birefringence None[1]
Dispersion 0.044[1]
Pleochroism None[1]
Ultraviolet fluorescence Colorless to yellowish stones; inert to strong in long wave, and typically blue. Weaker in short wave.[1]
Absorption spectra In pale yellow stones a 415.5 nm line is typical. Irradiated and annealed diamonds often show a line around 594 nm when cooled to low temperatures.[1]
Streak White
Specific gravity 3.52 (± 0.01)[1]
Density 3.5-3.53 g/cm³
Diaphaneity Transparent to subtransparent to translucent

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In mineralogy, diamond (from the ancient Greek ἀδάμας, adámas) is the allotrope of carbon where the carbon atoms are arranged in an isometric-hexoctahedral crystal lattice. After graphite, diamond is the second most stable form of carbon. Its hardness and high dispersion of light make it useful for industrial applications and jewelry. It is the hardest known naturally occurring mineral. It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds that are harder than the diamonds used in hardness gauges.[2] A material called lonsdaleite is confirmed to be 58 percent stronger than diamond and is the hardest material known to date.[3] Aggregated diamond nanorods, a material created using ultrahard fullerite (C60) is also harder than diamond, other substances such as cubic boron nitride, wurtzite boron nitride, rhenium diboride and ultrahard fullerite itself are comparable.

Diamonds are specifically renowned as a material with superlative physical qualities; they make excellent abrasives because they can be scratched only by other diamonds, borazon, ultrahard fullerite, rhenium diboride, or aggregated diamond nanorods, which also means they hold a polish extremely well and retain their lustre. Approximately 130 million carats (26,000 kg (57,000 lb)) are mined annually, with a total value of nearly USD $9 billion, and about 100,000 kg (220,000 lb) are synthesized annually.[4]

The name diamond is derived from the ancient Greek ἀδάμας (adámas), "unbreakable, untamed", from ἀ- (a-), "un-" + δαμάω (damáō), "to overpower, to tame"[5]. They have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history.[6][7] Popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. They are commonly judged by the “four Cs”: carat, clarity, color, and cut.

Roughly 49% of diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are mined from kimberlite and lamproite volcanic pipes, which can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface. The mining and distribution of natural diamonds are subjects of frequent controversy such as with concerns over the sale of conflict diamonds (aka blood diamonds) by African paramilitary groups.