Uneven, Uneven, Gemstones of the world (2001) More from other references
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
H 4Mg 3Si 2O 9Walter Schumann , Gemstones of the world (2001) More from other references
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.