ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009)
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(Ca,Mn2+ )Si 3O 9Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references
NaFe 3+ 3 Al 6 (BO 3 ) 3 Si 6 O 18 (O,F,OH) 4 Anthony et al, Handbook of mineralogy (2001)