Diamond is the purest form of natural carbon. It occurs as small crystals embedded in rocks. These are supposed to have been formed by the crystallization of carbon under extreme pressure and temperature in the interior of the earth. Nowadays, synthetic industrial diamonds are being manufactured by subjecting graphite to very high temperatures and pressures. Carbon atoms in diamond have tetrahedral structure. Each atom of carbon is surrounded by four other atoms that together forms the tetrahedral structure, as shown in the figure 10.1.
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South Africa is the largest producer of diamonds in the world and a pioneer in diamond mining. In India too, diamond deposits are found in certain areas especially in Golconda in Andhra Pradesh and Panna in Madhya Pradesh.
Physical Properties of Diamond
1. Diamond is the purest form of carbon.2. It is the densest of all allotropes of carbon (specific gravity is 3.51).
3. Diamond's tetrahedral structure, makes it the hardest naturally occurring substance. It is brittle and transparent.4. Pure diamond is colourless, but traces of dissolved impurities give it blue, green, yellow, red, or even black tinge. The black variety is called 'carbanado'. Although the coloured ones (except the black ones) are slightly impure, they have greater gem value.
5. Diamond has very high refractive index (2.415). When properly cut and polished, it allows the light to undergo total internal reflection that makes it very brilliant.6. It is transparent to light and X-rays. This property is used to identify a real diamond from a fake one, e.g., glass can be made to shine as brilliantly as diamond but it is opaque to X-rays.
7. Due to catenation there are no free electrons that can move in the structure of diamond. Hence it is a non-conductor of electricity, but extremely good conductor of heat.8. It is insoluble in all known solvents.
Chemical Properties of Diamond
1. Diamond is chemically very inert. It does not react with any substance at ordinary temperatures.2. When heated in oxygen to about 800oC, it completely burns to form carbon dioxide. This shows that diamond is pure form of carbon.
3. When heated in the absence of air to 1500oC, the atoms get rearranged to form graphite.4. Diamond is affected slowly by molten sodium carbonate, forming carbon monoxide.
5. When heated with concentrated sulphuric acid and potassium dichromate it gets oxidised to carbon dioxide.Uses of Diamond
1. Diamond is used as a gem (except the black variety) due to its brilliance.
2. Black variety of diamond is use for cutting glass, as drilling bits for industrial drills, for polishing other diamonds etc.