Handbook of mineralogy (2001), Difficult, Fibrous
UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009)
Ca 6Si 6O 17(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)
Ca 2(Mg,Al) 6(Si,Al,B) 6O 20Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references