Uneven, UnevenArthur Thomas, Gemstones (2009), Brittle
Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
MnPO 4Walter Schumann , Gemstones of the world (2001) More from other references
Na 3(Na,K)Al 4Si 4O 16Ulrich Henn and Claudio C.