Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Metallic
Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001)
Ca 2B 6O 11 · 5H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references
SiO 2Ulrich Henn and Claudio C.