ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
(Mg,Fe) 5(SiO 4) 2(F,OH) 2Ulrich Henn and Claudio C.