Today's diamond mines are located at ancient volcanoes. These volcanoes are not what formed the diamonds but are what brought them to the earth's surface. The diamonds are formed between 60 and 120 miles below the surface and can be found in the cooled magma, known as kimberlite. A volcano forms when molten magma reaches the surface. The volcano remains active as long as the magma is being forced to the surface. When the magma is no longer being pushed to the surface, the volcano is said to be dormant. The magma near the surface cools and solidifies in the pipe or tube formed when the magma was forced to the surface.

A volcano becomes extinct when the magma chamber many miles below the surface is depleted and has no more magma to send to the surface. These extinct volcano pipes are where the diamonds are found. Deep mining operations are used in these locations to extract the diamonds. As the earth's surface is weathered and eroded away, these deposits are washed down stream to form what is called placer deposits.