Diamond is the most precious and enduring substance in the world. It is the hardest material known so far. It cannot be cut by any metal or for that matter by any other thing except by another diamond only. Metal saw impregnated with diamond powder is used for cutting diamonds.
Diamond which is a pure crystalline form of carbon is obtained from mines. At 900°C, it starts burning slowly and combines with atmospheric oxygen to form carbon dioxide. At 1000° C, it gets converted into graphite. At higher temperatures the rate of formation of graphite is faster.
It is a good conductor of heat but a bad conductor of electricity. Its thermal conductivity is five times greater than that of copper. Diamonds vary in colour; they are either colourless or found in green, brown, white, yellow, pink and sometimes black.
Until 1955, diamond was obtained only from mines but later certain synthetic methods for its manufacture were also developed. Diamond obtained from mines is called natural diamond, whereas the one made by synthetic methods is called artificial diamond. Africa is the biggest source of natural diamonds. About 80% of these come from this continent. Before they come to the market for sale, they are cut into different shapes and polished. The shine of diamonds remains intact even after hundreds of years.
Synthetic diamonds were made for the first time in the world by the General Electric Co. of USA in 1955. In the synthetic process, diamonds are produced from graphite. In high temperature furnaces graphite is heated to about 3000° C under high pressure. By doing so graphite is converted into diamond. Synthetic diamond resembles the natural diamond in many respects. These are generally used in jewellery and industry. Industrial or inferior diamonds are also used for drilling and grinding. The weight of the diamond is measured in carats. One carat is equal to about 200 mg.