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Subconchoidal, Conchoidal, Brittle, ConchoidalArthur Thomas, Gemstones (2009)
NaFe 3+ 3 Al 6 (BO 3 ) 3 Si 6 O 18 (O,F,OH) 4 Anthony et al, Handbook of mineralogy (2001)
TiO 2Michael OâDonoghue , Gems, Sixth edition (2006) More from other references