Kimberlite
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Kimberlite is a mica peridotite and a source of rich deposits of diamonds. The deposits occurring at Kimberley, South Africa were the first recognized and the source of the name. The Kimberly 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."
Kimberlites are the result of explosive diatreme volcanism from very deep mantle derived sources. These volcanic explosions produce "kimberlite pipes," vertical columns of rock that rise from deep magma reservoirs. Kimberlites often contain chromium-bearing spinel, olivine, garnet, and other minerals which are known as indicator minerals for the presence of diamond.
References
- Kimberlite (http://www.eos.ubc.ca/research/diamonds/kopylova/introduction.html)
- Kimberlite hosted diamonds (http://www.em.gov.bc.ca/Mining/Geolsurv/MetallicMinerals/MineralDepositProfiles/profiles/n02.htm)de:Kimberlit