Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Brittle, Metallic
Handbook of mineralogy (2001), Difficult, Fibrous
CuSMichael OâDonoghue , Gems, Sixth edition (2006) More from other references
Ca 6Si 6O 17(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)