Not Available, Southern and central Africa
Afghanistan, Pakistan, Burma, Brazil, Madagascar, USA, Canada, Russia, Madagascar, Brazil, Canada, Mexico, Madagascar, Brazil, Canada, Mexico
ConchoidalGemdat.org, Management Team (2012), ConchoidalGemdat.org, Management Team (2012)
Gemstones of the world (2001), UnevenWalter Schumann, Gemstones of the world (2001)