Final Allocations Magnetite: Fe 2 O 3  0; FeO  10-2 = 8 FeO + MgO = 8 + 17 = 25 Diopside: CaO  0; FeO + MgO = 25 – 7 = 18; SiO 2  SiO 2 – 2CaO = 27-14 = 13 Hypersthene: FeO + MgO  0; SiO 2  13 – 18 = -5 (Call this -D) Olivine: Ol = D = 5 Hypersthene: Hy – 2D = 18 – 10 = 8
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