Uneven, UnevenArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Conchoidal, Splintery, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle
(Na,Ca) 8Al 6Si 6O 24(SO 4,S,Cl) 2Ulrich Henn and Claudio C.
AlPO4 · 2(H2O)