Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Subconchoidal, ConchoidalArthur Thomas, Gemstones (2009)
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.
(Fe,Mn)Ta 2O 6Walter Schumann , Gemstones of the world (2001) More from other references