Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle
Uneven, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Be 2SiO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
(Mg,Fe) 5(SiO 4) 2(F,OH) 2Ulrich Henn and Claudio C.