Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Uneven
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
ThCa 2Si 8O 20Walter Schumann , Gemstones of the world (2001) More from other references
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.