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Diamond
A scattering of round-brilliant cut diamonds shows off the many reflecting facets.
General
Category	Mineral
Formula (repeating unit)	C
Crystal system	Isometric-Hexoctahedral (Cubic)
Identification
Formula mass	12.01 gm
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
Cleavage	111 (perfect in four directions)
Fracture	Conchoidal - step like
Mohs scale hardness	10
Luster	Adamantine
Streak	Colorless
Diaphaneity	Transparent to subtransparent to translucent
Specific gravity	3.52 (+/- .01)
Density	3.5-3.53
Polish luster	Adamantine
Optical properties	Singly Refractive
Refractive index	2.4175-2.4178
Birefringence	none
Pleochroism	none
Dispersion	.044
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.

Diamond 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. About 130 million carats (26,000 kg) are mined annually, with a total value of nearly USD $9 billion. About 100,000 kg are synthesized annually.

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. 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 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, although in recent years the company's market share has dropped to below 50%.

Material properties

A diamond is a transparent crystal of tetrahedrally bonded carbon atoms. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness, its high dispersion index, and high thermal conductivity, with a melting point of 3820 K, which converts to 6416.33 F and 3546.85 C.

Hardness

Facetware.

Process

had better color appearance than non-fluorescent stones. Since blue is a complementary color to yellow and can appear to cancel it out, strong blue fluorescence had especially better color appearance with lower color graded diamonds that have a slight yellowish tint such as "I" color or "J" color but had little effect on the more colorless "D" through "F" color grades.

Cleaning

Cleanliness heavily affects a diamond's beauty. A clean diamond is more brilliant and fiery than the same diamond when it is "dirty". Dirt or grease on the top of a diamond reduces its luster. Water, dirt, or grease on the bottom of a diamond interferes with the diamond's brilliance and fire. Even a thin film absorbs some light that could have been reflected to the person looking at the diamond. Colored dye or smudges can affect the perceived color of a diamond. Historically, some jewelers' stones were misgraded because of smudges on the girdle, or dye on the culet. Current practice is to clean a diamond thoroughly before grading its color.

Maintaining a clean diamond can sometimes be difficult as jewelry settings can obstruct cleaning efforts and oils, grease, and other hydrophobic materials adhere well to a diamond's surface. Many jewelers use steam cleaners. Some jewelers provide their customers with ammonia-based cleaning kits; ultrasonic cleaners are also popular.

History

1. ^ Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
2. Yarnell, Amanda (2004). "The Many Facets of Man-Made Diamonds". Chemical and Engineering News. 82 (5). American Chemical Society: 26–31. ISSN 0009-2347. Retrieved 2006-10-03.
3. Pliny the Elder. Natural History: A Selection. Penguin Classics. pp. p. 371. ISBN 0140444130. {{cite book}}: |pages= has extra text (help)
4. Cite error: The named reference ancient_China was invoked but never defined (see the help page).
5. "A Contribution to the Understanding of Blue Fluorescence on the Appearance of Diamonds" (PDF). GIA. GIA. Winter 1997. {{cite web}}: Unknown parameter |accessmonthday= ignored (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)