ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.