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