Uneven, Uneven, ConchoidalWalter Schumann, Gemstones of the world (2001)
UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
Mg 2Al 4Si 5O 18Ulrich Henn and Claudio C.
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.