ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Be 2BO 3(OH)Ulrich Henn and Claudio C.
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references