ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Splintery
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), 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
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references