DIAMONDS The best-known of all gems, diamonds are an extremely hard crystalline form of carbon which
is created under enormous heat and pressure deep within the earth's crust. India was originally the main source of diamonds, followed by Brazil from about 1750. In 1867, they were discovered in South Africa, which now dominates the market.
Diamonds are measured by weight in carats - stones can be as small as
1/32 of a carat - and graded by colour. The most valuable ones are blue-white, and are known as diamonds of the first water. Next come the colourless variety, which have a hard whiteness. Stones with a yellow to brown tinge are less valuable.
Occasionally 'sports' turn up. These are diamonds in unusual colours such as canary yellow, bronze, blue, green, pink and even red. Green diamonds can also be created artificially by treating normal stones with radium.
The glittering, flashing quality of a diamond is partly due to the stone's nature and partly to the cutting employed.
Any cutting or cleaving must go with the grain of the stone if it's to retain its sparkle. Irregular or flawed stones can be sawed against the grain or in any desired direction. Before the 16th century, diamonds were often left in their natural state, which allowed little refraction and showed the stone as rather dull.