ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Splintery
UnevenArthur Thomas, Gemstones (2009) Tough, UnevenArthur Thomas, Gemstones (2009) Tough, Brittle, Uneven
Na 4Al 3Si 9O 24Cl to Ca 4Al 6Si 6O 24(CO 3,SO 4)Walter Schumann , Gemstones of the world (2001) More from other references
Mn 8Si 6O 15(OH,Cl) 10Ulrich Henn and Claudio C.