Afghanistan, Brazil, Southern and central Africa, Madagascar, Russia, USA, Zimbabwe
China, Russia
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, Conchoidal, Brittle, Metallic, ConchoidalArthur Thomas, Gemstones (2009)