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Saturday, October 27, 2007

Diamond : as a mineral

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.
Crystal habit Octahedral
Crystal system Isometric-Hexoctahedral (Cubic)
Cleavage 111 (perfect in four directions)
Fracture Conchoidal - step like
Mohs Scale hardness 10[1]
Luster Adamantine
Polish luster Adamantine
Refractive index 2.4175–2.4178
Optical Properties Singly Refractive
Birefringence none
Dispersion .044
Pleochroism none
Ultraviolet fluorescence colorless to yellowish stones - inert to strong in long wave, and typically blue. Weaker in short wave.
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.
Streak White
Specific gravity 3.52 (+/- .01)
Density 3.5-3.53
Diaphaneity Transparent to subtransparent to translucent
Diamond is an allotrope of carbon. It is the hardest known natural material and the third-hardest known material after aggregated diamond nanorods and ultrahard fullerite. Its hardness and high dispersion of light make it useful for industrial applications and jewelry.

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, or aggregated diamond nanorods, which also means they hold a polish extremely well and retain their lustre. Approximately 130 million carats (26,000 kg) are mined annually, with a total value of nearly USD $9 billion, and about 100,000 kg are synthesized annually.[2]

The name diamond derives from the ancient Greek adamas (αδάμας; “invincible”). They have been treasured as gemstones since their use as religious icons in ancient India and usage in engraving tools also dates to early human history.[3][4] 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 brought to the surface the diamond crystals from 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 (aka blood diamonds) by African paramilitary groups.

references :
1.^ a b c d e f g h i j k Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
Yarnell, Amanda (2004). "The Many Facets of Man-Made Diamonds". Chemical and Engineering News 82 (5): 26–31. American Chemical Society. ISSN 0009-2347. Retrieved on 2006-10-03
3.Pliny the Elder. Natural History: A Selection. Penguin Classics, p. 371. ISBN 0140444130
4."Chinese made first use of diamond", BBC News, 17 May 2005. Retrieved on 2007-03-21
5.Wikipedia,the free encyclodepia


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