Uneven, UnevenArthur Thomas, Gemstones (2009), Conchoidal, Brittle
Splintery, Granular, Splintery, Granular, Gemstones (2009)
(Na,Ca) 8Al 6Si 6O 24(SO 4,S,Cl) 2Ulrich Henn and Claudio C.
Ca 2(Mg,Fe) 5(OH) 2Walter Schumann , Gemstones of the world (2001) More from other references