ETYM Old Eng. diamaund, diamaunt, French diamant, corrupted, from Latin adamas, the hardest iron, steel, diamond. Related to Adamant, Tame.
1. Very hard native crystalline carbon valued as a gem; SYN. adamant.
2. A transparent piece of diamond that has been cut and polished and is valued as a precious gem.
Generally colorless, transparent mineral, an allotrope of carbon. It is regarded as a precious gemstone, and is the hardest substance known (10 on the Mohs' scale). Industrial diamonds, which may be natural or synthetic, are used for cutting, grinding, and polishing.
Diamond crystallizes in the cubic system as octahedral crystals, some with curved faces and striations. The high refractive index of 2.42 and the high dispersion of light, or “fire”, account for the spectral displays seen in polished diamonds.
History.
Diamonds were known before 3000 BC and until their discovery in Brazil 1725, India was the principal source of supply. Present sources are Australia, Zaire, Botswana, Russia (Yakut), South Africa, Namibia, and Angola; the first two produce large volumes of industrial diamonds. Today, about 80% of the world's rough gem diamonds are sold through the De Beers Central Selling Organization in London.
Sources.
Diamonds may be found as alluvial diamonds on or close to the Earth’s surface in riverbeds or dried watercourses; on the sea bottom (off SW Africa); or, more commonly, in diamond-bearing volcanic pipes composed of “blue ground”, kimberlite or lamproite, where the original matrix has penetrated the Earth’s crust from great depths. They are sorted from the residue of crushed ground by X-ray and other recovery methods.
Varieties.
There are four chief varieties of diamond: well-crystallized transparent stones, colorless or only slightly tinted, valued as gems; boart, poorly crystallized or inferior diamonds; balas, an industrial variety, extremely hard and tough; and carbonado, or industrial diamond, also called black diamond or carbon, which is opaque, black or gray, and very tough. Industrial diamonds are also produced synthetically from graphite. Some synthetic diamonds conduct heat 50% more efficiently than natural diamonds and are five times greater in strength. This is a great advantage in their use to disperse heat in electronic and telecommunication devices and in the production of laser components.
Practical uses.
Because diamonds act as perfectly transparent windows and do not absorb infrared radiation, they were used aboard NASA space probes to Venus 1978. The tungsten-carbide tools used in steel mills are cut with industrial diamond tools.
Cutting.
Rough diamonds are often dull or greasy before being polished; around 50% are considered “cuttable” (all or part of the diamond may be set into jewelry). Gem diamonds are valued by weight (carat), cut (highlighting the stone’s optical properties), color, and clarity (on a scale from internally flawless to having a large inclusion clearly visible to the naked eye). They are sawn and polished using a mixture of oil and diamond powder. The two most popular cuts are the brilliant, for thicker stones, and the marquise, for shallower ones. India is the world’s chief cutting center.
Noted rough diamonds include the Cullinan, or Star of Africa (3,106 carats, over 500 g/17.5 oz before cutting, South Africa, 1905); Excelsior (995.2 carats, South Africa, 1893); and Star of Sierra Leone (968.9 carats, Yengema, 1972).

A playing card in the minor suit of diamonds.

Of, relating to, or being a 60th or 75th anniversary or its celebration

1. Town in Missouri (USA); zip code 64840.
2. Village in Illinois (USA).
3. Kumgang, mountains SE North Korea; highest 5374 feet (1638 meters).

To adorn with or as if with diamonds.