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Diamond

Diamond is one of the natural allotropes of carbon (the main one being graphite). Sometimes known as adamant, it is the hardest known naturally occurring material, scoring 10 on the old Mohs hardness scale. The material boron nitride, when in a form structurally identical to diamond, is nearly as hard as diamond; a currently hypothetical material, beta carbon nitride, may also be as hard or harder in one form. The diamond derives its name from the Greek adamas, "untameable" or "unconquerable", referring to its hardness.

Diamond is a transparent crystal with a refractive index of 2.417, a high dispersion of 0.044, and a specific gravity of 3.52. Diamonds have a cubic crystal system[?] consisting of tetrahedrally bonded carbon atoms. Diamonds have a perfect octahedral cleavage, which means that they have 4 cleavage planes. They sometimes have an conchoidal (like glass) fracture, sometimes irregular. The lustre of a diamond is described as adamantine, which simply means diamond-like.

Diamonds exhibit fluorescence of various colors under long wave ultra-violet light, but generally bluish-white, yellowish or greenish fluorescence under X-rays. Diamonds have a violet absorption spectrum[?] at 415.5 nm. Colored stones show additional violet bands. Brown diamonds show a green band at 504 nm, sometimes accompanied by 2 additional weak green bands.

Except for natural blue diamonds which are semiconductors, diamond is a good electrical insulator, but unlike most insulators, is a good conductor of heat because of the strong bonding within the molecule. Specially purified artificial diamonds have the highest thermal conductivity (20-25 W/cmK, five times more than copper) of any known solid at room temperature. Natural blue diamonds contain boron atoms which replace carbon atoms in the crystal matrix, and also have high thermal conductance. Because diamonds have such high thermal conductance they are already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating. Natural blue diamonds and synthetic diamonds doped with boron are p-type semiconductors[?]. If an n-type semiconductor[?] can be synthesized, electronic circuits could be manufactured of diamond. Worldwide research is in progress, with occasional successes reported, but nothing definite. In 2002 it was reported in the journal Nature that researchers have succeeded in depositing a thin diamond film on a diamond surface which is a major step towards manufacture of a diamond chip.

Type I diamonds have nitrogen atoms as the main impurity. If they are in clusters they do not affect the diamond's color (Type Ia). If dispersed though out the crystal they give the stone a yellow tint (Type Ib), the Cape series. Typically a natural diamond crystal contains both Type Ia and Type Ib material. Synthetic diamonds which contain nitrogen are Type Ib

Type II diamonds have no nitrogen impurities. Rarely, they contain no other impurities (Type IIa). Type IIb are the natural blue diamonds which contain scattered boron within the crystal matrix.

Diamonds occur in a variety of colors - steel, white, blue, yellow, orange, red, green, pink, brown and black. Colored diamonds contain impurities that cause the coloration, pure diamonds are always translucent and colorless.

In the late 18th century, diamonds were demonstrated to be made of carbon by the rather expensive experiment of igniting a diamond (by means of a burning-glass) in an oxygen atmosphere and showing that carbonic acid gas (carbon dioxide) was the product of the combustion. The fact that diamonds are combustible bears further examination because it is related to an interesting fact about diamonds. Diamonds are carbon crystals that form deep within the Earth under high temperatures and extreme pressures. At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (ΔH = -2KJmol^-1). So, despite De Beers' ad campaign, diamonds are definitely not forever. However, owing to a very large kinetic energy barrier, diamonds will not decay into graphite under normal conditions.

Table of contents

1 The Diamond Industry

2 Symbolism of Diamonds

1 Famous Stones
2 External Links
3 Further Reading

The Diamond Industry

Due to their high dispersion (play of color), diamonds have been prized as a constituent of jewellery, and a large trade in gemstone-class diamonds exists, mostly controlled by the De Beers company, which has used its monopoly to control prices.

Marcel Tolkowsky's 1919 book on Diamond Design (http://www.folds.net/diamond/index) describes the history of diamond cutting since the late Middle Ages. Roughly 1900, the development of diamond saws and good jewelry lathes enabled the modern Round Brilliant cut. Tolkowsky determined a detailed design for this cut. His geometric calculations are in his book.

In the 1970s, Bruce Harding developed another mathematical model for gem design. Since then, several groups have used computer models (e.g., MSU, OctoNus (http://www.cutstudy.com), GIA (http://www.gia.org), and folds.net (http://www.folds.net/diamond/index)) and specialized scopes to design diamond cuts.

During the 1990s Israeli interests acquired about 20% of the diamond trade, buying diamonds from Russia and from mines in Africa not controlled by De Beers. De Beers now deals only in diamonds from their own mines. A major diamond cutting industry has grown up in Gujarat State, India where 90% of the world's diamonds are cut by a workforce of 800,000. Diamonds are valued according to the four C's of diamond grading, namely color, clarity, cut, and carat. Deep blue diamonds such as the Hope Diamond are particularly valuable as are blue-white diamonds generally.

80% of the diamonds produced are poorer quality (discolored, less transparent) diamonds which are used as industrial diamonds, where their extreme hardness is useful in cutting and grinding otherwise intractable materials (including other diamonds). Lately, gas-phase deposition processes have been devised that allow thin diamond films to be grown on some surfaces, greatly increasing the durability of some machine tools.

Diamonds typically have cubic symmetry. A second form called lonsdaleite with hexagonal symmetry is also found. The local environment of each atom is identical in the two structures.

Historically diamonds were found in alluvial deposits in southern India which are now worked out. Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo and Sierra Leone. Revolutionary groups in some of those countries have taken control of diamond mines, using the conflict diamonds to finance their continuing operations with baleful results. There are also commercial deposits in the Northwest Territories, Canada in the Russian Arctic, Brazil and in Northern and Western Australia. Occasionally diamonds have been found in glacial deposits in Wisconsin and Indiana. The Wisconsin finds can be explained by recent Canadian discoveries, but the diamonds found in Indiana must have come from an as yet undiscovered source in Quebec as the movement of ice was from northeast to southwest.

Diamonds were first produced artificially on February 16, 1953 in Stockholm, Sweden by the QUINTUS project of ASEA, Sweden's major electrical manufacturing company using a bulky apparatus designed by Baltzar von Platen. Pressure was maintained within the device at an estimated 83,000 atmospheres for an hour. A few small crystals were produced. The discovery was kept secret. Thus far no commercially viable process has produced diamonds indistinguishable from natural gemstones but the quality of artificial diamonds has improved over time.

A city of major importance in diamond trade is Antwerp.

Symbolism of Diamonds

Diamonds are often used to symbolize love and are often found in wedding bands.

Famous Stones

External Links

On conflict diamonds (UN) (http://www.un.org/peace/africa/Diamond)
Article in Nature on the diamond chip (http://www.nature.com/nsu/020902/020902-9)
Article in Nature on advancing techniques of growing diamond crystals (http://www.nature.com/nsu/020923/020923-17)
OctoNus Software (http://www.cutstudy.com) has posted several diamond cut studies, by various authors. OctoNus, Moscow State University, Bruce Harding, and others have posted work there.
Gemological Institute of America (http://www.gia.org)

Further Reading

Diamond Design (http://www.folds.net/diamond/index), Marcel Tolkowsky. Web edition as edited by Jasper Paulsen. www.folds.net, Seattle, 2001.
The New Alchemists: Breaking Through the Barriers of High Pressure, Robert M. Hazen, Times Books, Random House, New York, 1992, hardcover, 286 pages, ISBN 0-8129-2275-1