The word diamond is derived from Greek word adamas means unbreakable. Diamond is an allotrope of carbon. It is the hardest substance crystallizes with cubic system. Diamond has the highest hardness and thermal conductivity of any bulk material. Even though diamond is the hardest substance it is not impervious. Diamond is formed by the strong covalent bonding between its atoms. And it has very rigid lattice due to this very less possibility of impurities present in it. Small amount of impurities present are boron and nitrogen. Blue diamonds are natural semiconductors, in contrast to most diamonds, which are excellent electrical insulators. The conductivity and blue color originate from boron impurity. Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band.
Diamond crystal is classified into 2 types
a) Crystalline gem variety b) Crypto-crystalline
Crystalline gem diamond is mainly used in ornaments.
Crypto-crystalline diamond is an industrial diamond used in industries for drilling, and cutting.
This is again devided into 3 types
1. Bort, boart or bortz
2. Carbonado- Its a compact variety of diamond. It has very close aggregates of very small crystals which are very tough.
3. Ballas- This is also known as black diamond. It has rounded edges or oval or radial structure of stones.


Diamonds are mainly formed at very high pressure and temperature conditions which founds at the depth of 140 to 190 Km in earth mantle. Diamonds are brought close to the Earth surface through deep volcanic eruptions by a magma, which cools into igneous rocks known as kimberlites and lamproites. Central and Southern African countries are the main sources of diamond contributing upto 50% of the total deposits throught the world. South Africa is having the biggest deposits of diamond. Other places of diamond deposits have been discovered in Canada, India, Russia, Brazil, and Australia.


Diamond is found in different colours like white, pale yellow, red, green, black, blue, pink.
Its crystal system is isometric-Hex octahedral.
Cleavage is perfect in four directions forming octahedrons.
Luster is adamantine to waxy and sometimes greasy.
Streak is white to colourless.
Its crystal habit is isometric which forms cubes and octahedrons.
Hardness of diamond is a perfect 10.
Specific gravity is slightly higher than 3.5.
Density is 3.5 to 3.53 g/cm3.
Melting point of diamond is 3820 degrees Kelvin.
Diamond is transparent over a larger range of wavelengths.
Blue diamonds are natural semiconductors which are excellent electrical insulators.


Industrially diamond is used where there is high degree of precision for cutting is required shape.
Diamonds are also used to polish the material.
Diamond has applications in industries as drill bits and saws.
Its powder is also used as an abrasive.
Diamond lathe tools are usedin the turning aircraft and engine parts.


1. Diamond is an allotrope of what?
Ans : Carbon.

2. Who is is the major contributor of diamond?
Ans : South Africa is the major contributor of diamond.

3. How is the cleavage of diamond?
Ans : Cleavage is perfect in four directions forming octahedrons.

4. What is the streak of diamond?
Ans : Streak is white to colourless.

5. Mention few applications of diamond?
Ans : Industrially diamond is used for cutting and grinding tools. Its powder is also used as an abrasive.


Industrial Minerals By R.K Sinha

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