An igneous rock that is ultrabasic
(containing very little silica); a type of
alkaline peridotite (see peridot) containing
mica in addition to olivine and other
minerals. Kimberlite represents the world's
principal source of diamonds. Kimberlite is
found in carrot-shaped pipelike intrusions
called diatremes, where mobile material from
very deep in the Earth's crust has forced
itself upwards, expanding in its ascent. The
material, brought upwards from near the
boundary between crust and mantle, often
altered and fragmented, includes diamonds.
Diatremes are found principally near
Kimberley, South Africa, from which the name
of the rock is derived, and in the Yakut area
of Siberia, USSR.