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