UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Splintery, UnevenArthur Thomas, Difficult, Fibrous
Ca 2B 5SiO 9(OH) 5Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
NaAlSi 2O 6Ulrich Henn and Claudio C.