Diamond is virtually the hardest substance known to man. It gets its name from the Ancient Greek word adamantos, meaning 'invincible'. The only mineral that is harder is the very rare lonsdaleite formed in meteorite impacts. Like graphite
and lonsdaleite, diamond is pure carbon. It glitters like glass because it has been transformed by enormous
pressure underground. It is now possible to make diamonds artificially be squeezing graphite under . extreme pressure. But pressures like these are rare in nature, occurring only deep in the Earth's crust and upper mantle. All diamonds found today are extremely old, being formed at least a billion years ago, with some more than three billion years old!
They formed at least 145km/90 miles below the Earth's surface and were gradually carried up in pipes of hot magma. These volcanic pipes cooled to form blue rocks called kimberlites and lamproites, which are the source of most of the world's best diamonds. Diamonds can easily be weathered out of kimberlitesto be washed awa y by streams into placer deposits. In their rough state diamonds look dull and it was only when jewellers began to cut them in the Middle Ages