ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Uneven, UnevenArthur Thomas, Gemstones (2009), Splintery
SiO 2Ulrich Henn and Claudio C.
Ca 2(Mg,Fe) 5Si 8O 22(OH) 2Ulrich Henn and Claudio C.