If diamonds are formed deep down in the earth, how do they get to the surface? Volcanoes - that's how. When they erupt, diamonds are thrown out of the top in the lava or are left in the pipe, the central, vertical part of the volcano. So the best place to find diamonds is in the center of an extinct volcano, in a type of rock called kimberlite. Kimberlite is named after the town of Kimberley in South Africa, where diamonds were first mined in the 1870's and some of the world's largest diamonds are still produced today.

An erupting volcano, showing the vertical pipe. © Gemological Institute of America. Reprinted by permission.

These pictures show diamond mines in the centers of extinct volcanoes. They have to dig down through the kimberlite pipe to find the diamonds. The kimberlite pipe at the Kimberley diamond mine in South Africa is mined to depths over 1,000 m (3,500 ft) below the surface.

'The 'Big Hole' at Kimberley, South Africa © De Beers

Aerial view of the Koffiefontein diamond mine, South Africa, operated by De Beers. © De Beers

Diamond is also found in rivers and streams or rocks around extinct volcanoes. This is because the igneous rock that makes up the volcano gets worn away by wind and rain over the years. Pieces of the igneous rock and diamond are carried down by the wind or in streams and rivers and, over many years, can get stuck together with lots of other pieces of sand and clay to form sedimentary rocks.