Handbook of mineralogy (2001), Difficult, Fibrous
Conchoidal, Uneven, ConchoidalArthur Thomas, Gemstones (2009)
Ca 6Si 6O 17(OH) 2Michael OâDonoghue , Gems, Sixth Edition (2006)
(Mg,Fe2+ )Al 2O 4Gemdat.org , Management Team (2012) More from other references