Splintery, UnevenArthur Thomas, Difficult, Fibrous
Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Metallic
NaAlSi 2O 6Ulrich Henn and Claudio C.
Ca 2B 6O 11 · 5H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references