Diamond, a mineral composed of pure carbon.
It is the hardest naturally
occurring substance known; it is also the most popular gemstone. Because
of their extreme hardness, diamonds have a number of important industrial
applications.
Diamond (gem)
country mine production 2006 (carats)* % of world mine production
*Estimate.
**Detail does not add to total given because of rounding.
Source: U.S. Department of the Interior, Mineral Commodity Summaries 2007.
Australia 25,000,000 29.4
Congo (Kinshasa) 24,000,000 28.2
Russia 15,000,000 17.6
South Africa 9,000,000 10.6
Botswana 8,000,000 9.4
China 1,000,000 1.2
United States 300,000 0.4
other countries 3,000,000 3.5
world total 85,000,000 100**
The hardness, brilliance, and sparkle of diamonds make them unsurpassed
as gems. In the symbolism of gemstones, the diamond represents steadfast
love and is the birthstone for April. Diamond stones are weighed in carats
(1 carat = 200 milligrams) and in points (1 point = 0.01 carat). In addition
to gem-quality stones, several varieties of industrial diamonds occur,
and synthetic diamonds have been produced on a commercial scale since
1960. See also industrial diamond; synthetic diamond.
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alluvial diamond mining
Alluvial diamond mining at Kenema, Sierra Leone
alluvial diamond mine
Large alluvial diamond mine near the Bow River in Western Australia.(more)
diamond mine in Kimberley
A diamond mine at Kimberley, South Africa.
History of diamond mining in South Africa
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Diamonds are found in three types of deposits: alluvial gravels, glacial tills,
and kimberlite pipes. The kimberlite pipes (such as those at Kimberley,
South Africa) form from intrusions of magma into the Earth’s crust and
deliver diamonds and other rocks and minerals from the mantle. The pipes
themselves are often less than 100 million years old. However, the
diamonds they carry were formed 1 to 3.3 billion years ago at depths of
more than about 75 miles (120 km). Diamonds found in alluvial and glacial
gravels must have been released by fluvial or glacial erosion of the
kimberlite matrix and then redeposited in rivers or in glacial till.
Diamonds vary from colourless to black, and they may be transparent,
translucent, or opaque. Most diamonds used as gems are transparent and
colourless or nearly so. Colourless or pale blue stones are most valued, but
these are rare; most gem diamonds are tinged with yellow. A “fancy”
diamond has a distinct body colour; red, blue, and green are rarest, and
orange, violet, yellow, and yellowish green more common. Most industrial
diamonds are gray or brown and are translucent or opaque, but better-
quality industrial stones grade imperceptibly into poor quality gems. The
colour of diamonds may be changed by exposure to intense radiation (as
released in a nuclear reactor or by a particle accelerator) or by heat
treatment.
A very high refractive power gives the diamond its extraordinary brilliance.
A properly cut diamond will return a greater amount of light to the eye of
the observer than will a gem of lesser refractive power and will thus appear
more brilliant. The high dispersion gives diamonds their fire, which is
caused by the separation of white light into the colours of the spectrum as it
passes through the stone.
The scratch hardness of diamond is assigned the value of 10 on the Mohs
scale of hardness; corundum, the mineral next to diamond in hardness, is
rated as 9. Actually, diamond is very much harder than corundum; if the
Mohs scale were linear, diamond’s value would be about 42. The hardness
of a diamond varies significantly in different directions, causing cutting and
polishing of some faces to be easier than others. For detailed physical
properties, see native element (table).
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How diamonds can be made from methane
Learn about manufacturing diamonds for use in research.
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In the atomic structure of diamond, as determined by X-ray
diffraction techniques, each carbon atom is linked to four equidistant
neighbours throughout the crystal. This close-knit, dense, strongly bonded
crystal structure yields diamond properties that differ greatly from those
of graphite, native carbon’s other form.
