Splintery, UnevenArthur Thomas, Difficult, Fibrous
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Conchoidal, Brittle
NaAlSi 2O 6Ulrich Henn and Claudio C.
MgAlBO 4Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references