Uneven, Uneven, Gems, Difficult, Fibrous
ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
Al 2O 3Arthur Thomas , Gemstones (2009)
NaAl 3(PO 4) 2(OH) 4 · 2H 2OMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references