Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle
UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Be 2SiO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
Ca 2B 5SiO 9(OH) 5Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references