Kimberlite

Kimberlite is a mica peridotite[?] which occurs at Kimberly, South Africa[?], the source of rich deposits of diamonds. These diamonds were originally found in decomposed kimberlite which was colored yellow by limonite, and so was called "yellow ground." Deeper workings encountered less altered rock, undecomposed kimberlite, which miners call "blue ground."

Kimberlite occurs in "kimberlite pipes," vertical columns of rock that rise from deep magma resevoirs.

See also: List of minerals