The name Diamond comes from the Greek word Adamas meaning indestructible. Diamonds are the hardest rock on Earth.
Diamonds form between 120 – 200km below the surface, in the Earth’s mantle, in patches amongst mantle rocks called peridotites and eclogites. Study of these rocks tell us that the material from which diamonds form is sea floor from 2-3 billion years ago that has been subducted into the mantle. These rocks are then subjected to temperatures over 10000°C and high pressures.
Diamonds are brought to the surface by eruptions from deep within the Earths mantle. The rocks form Kimberlite pipes, which are very rare. Such eruptions bring to the surface a sample of the rocks found within the mantle and are the main source of information about the centre of the Earth. These exotic pieces of rock are called xenoliths. The explosions occasionally pass through these patches bringing diamonds to the surface as xenoliths. Diamonds only survive if brought to the surface quickly. If they travel slowly to the surface they turn into graphite.
Kimberlite pipes found within very old continental crust, underlain by cold mantle have the highest chance of containing diamonds, but a kimberlite pipe could form anywhere at any time.
