Uneven, UnevenArthur Thomas, Gemstones (2009), Splintery
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Ca 2(Mg,Fe) 5Si 8O 22(OH) 2Ulrich Henn and Claudio C.
Al 2Be 3Si 6O 18Martin H.