ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle
SiO 2Ulrich Henn and Claudio C.
Be 2SiO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references