What is a Diamond?
A diamond is a crystal completely made of the element carbon, except for trace impurities like boron and nitrogen. The arrangement of the carbon atoms or its crystal structure within the diamond gives it its unique properties. As well as being the hardest known material, it is also the least compressible, and the stiffest material, the best thermal conductor with an extremely low thermal expansion, chemically inert to most acids and alkalis, immensely strong, rigid structure with a very high melting point (3800°C) diamond is the hardest known natural substance.
How are Diamonds formed?
Diamonds are not created from the compressed trees and vegetation that produce coal as popularly thought. Experiments and the high density of diamonds show they can only form while under tremendous heat and pressure. The only places where these types of conditions exist are deep beneath the Earth s surface, about 150km to200km (90 to 120 miles) in a region beneath the crust known as the mantle where there is an abundance of carbon atoms. The pressure here combined with temperatures ranging from 900 to 1300 on the Celsius scale forced the carbon atoms together to crystallise in a cubic (isometric) arrangement creating diamonds.
How did they get nearer the surface?
The diamonds and other substances from Earth s mantle are transported in magma that rises in a carrot-shaped "pipe" and erupts in small but violent volcanoes. The pipe is composed of a volcanic rock called kimberlite named after the city of Kimberley, South Africa, where the pipes were first discovered in the 1870s. Another rock that provides diamonds is lamproite. Geologists look for certain "indicator"minerals among the gravel of regions they think may host diamond-bearing pipes.