Conchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Uneven, UnevenArthur Thomas, Gemstones (2009), Brittle
(Be,Cs) 3Al 2Si 6O 18 · 0.5H 2OUlrich Henn and Claudio C.
MnPO 4Walter Schumann , Gemstones of the world (2001) More from other references