ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
Be 2BO 3(OH)Ulrich Henn and Claudio C.
BaSO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references