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Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle
NaFe 3+ 3 Al 6 (BO 3 ) 3 Si 6 O 18 (O,F,OH) 4 Anthony et al, Handbook of mineralogy (2001)
Pb 5(AsO 4) 3ClMichael OâDonoghue , Gems, Sixth Edition (2006) More from other references