ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
SiO 2(+Al 2O 3)Walter Schumann , Gemstones of the world (2001)
(Fe,Mn) 7Si 7O 21Ulrich Henn and Claudio C.