ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
Na 3(Na,K)Al 4Si 4O 16Ulrich Henn and Claudio C.