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Allotropy is the phenomenon exhibited by some elements, whereby an element can exist in various forms, which differ only in their physical properties but possess the same chemical properties. These various forms of the element are called allotropes. Carbon, phosphorus and sulphur are some of the non-metals that show allotropy. Diamond, graphite and amorphous carbon are the allotropic forms of carbon.

Like carbon, other elements like phosphorous, sulphur, oxygen, tin, etc., show allotropy. Ozone is an allotrope of oxygen.

Diamond occurs in all shapes and sizes. Even though it is a sparkling material it is made up of carbon which is black. The shine in diamond is based on its definite crystalline arrangement. When carbon is trapped in molten lava of volcanoes at a depth of over 150 km diamond crystals are formed. At this depth, the temperature and pressure are very high. These conditions convert carbon into diamond. Diamond reaches the upper surface of the earth along with kimberlitic rocks.


Each carbon atom in diamond is bonded to four carbon atoms, which in turn are again bonded to four carbon atoms each. This arrangement gives rise to a closely packed, hard, three-dimensional structure, which makes diamond the hardest natural substance.

Diamond can also be made artificially from graphite. If graphite is subjected to a very high pressure at very high temperature, diamonds can be produced in small sizes. The diamond is measured in carats. This carat is different from the carat used to describe the quality of gold. The Kohinoor diamond weighs 106 carats. 


Diamond deposits have been found in South Africa, Ghana, Angola, India, Brazil and Eastern Siberia. In India, diamonds are found in Panna (Madhya Pradesh), Wajrakarur (Andhra Pradesh) and Golconda (Karnataka). The famous Kohinoor diamond was found in Wajrakarur.


Properties of Diamond

  • Diamond is a transparent solid. It is usually colourless, but we can impart colour to diamonds by adding small amount of impurities.
  • It is a non-conductor of heat.
  • It is a poor conductor of electricity.
  • It has a high density of 3.5 g/cm3.
  • It has a high refractive index of 2.5.
  • It burns to give carbon dioxide at 800oC.
  • It is the hardest natural substance. One can cut a diamond with only diamond.
Uses of Diamond
  • It is used in jewellery because the properly cut and polished diamond sparkles brightly.
  • It is used to make radiation proof windows in space satellites.
  • It is used to cut glass.
  • It is used for cutting and drilling of rocks.

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