ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Conchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001), Brittle
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
Be 2SiO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references