Morimotoite, Ca3TiFe2+Si3O12, a new titanian garnet from Fuka, Okayama Prefecture, Japan

Abstract

AbstractMorimotoite, Ca3TiFe2+Si3O12, has been found in contaminated rocks which are considered to be a kind of endoskarn at Fuka, Bitchu-Cho, Okayama Prefecture, Japan. Morimotoite is derived from andradite, , by the substitution Ti + Fe2+ = 2Fe3+. It is associated with calcite, vesuvianite, grossular, wollastonite, hematite, prehnite, fluorapatite, perovskite, zircon, baddeleyite and calzirtite. It is cubic with space group Ia3d. The unit cell dimension a is 12.162(3) Å. Its refractive index n is 1.995(2) and the density 3.75(2) g cm−3 (meas.), 3.80 g cm−3 (calc.). The Mohs' hardness is 7.5. Calculation of the analytical data on the basis of twelve oxygen atoms and eight cations shows that this mineral has a simplified chemical formula Ca3(Ti,Fe2+Fe3+)2(Si,Fe3+)3O12 where Ti > Fe2+ > 0.5. Morimotoite was synthesized at low oxygen fugacities, 650 and 700°C and 1 kbar total pressure.