UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.
SiO 2Ulrich Henn and Claudio C.