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Uneven, ConchoidalArthur Thomas, Gemstones (2009), Brittle, Metallic
Na x[Fe2+2(Al,Fe3+ )]Al 6(BO 3) 3Si 6O 18(OH) 4Anthony et al , Handbook of mineralogy (2001)
Mg 2Si 2O 6Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references