Uneven, Splintery, Conchoidal, UnevenWalter Schumann, Gemstones of the world (2001)
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
SiO2
(K,Cs)Al 4Be 4(B,Be) 12O 28Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references