Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
Subconchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009), Irregular
Al 6B 5O 15(F,OH) 3Ulrich Henn and Claudio C.
SnO 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references