Momoiite, (Mn2+,Ca)3(V3+,Al)2Si3O12, an Mn2+- and V3+-rich analog of silicate garnet, was found in three localities: the Kurase (type locality), Hokkejino, and Fujii mines that are respectively located in Ehime, Kyoto, and Fukui Prefectures, Japan. Momoiite is greenish-yellow to emerald-green in color, and it occurs in the form of an aggregate having a size of up to 1 mm in a vein having a thickness of several millimeters with calcite and tephroite. Momoiite is optically isotropic, with n = 1.86(1). Its calculated density is 4.01 g/cm3, and its hardness on the Mohs scale is 6.5. The representative empirical formula of momoiite from the Kurase mine is (Mn1.80Ca1.12Mg0.04)Σ2.96(V1.51Al0.52)Σ2.03Si3.00O12 on the basis of O = 12 per formula unit. The mineral is cubic with a space group of Ia3d, a = 11.9242(7) Å, V = 1695.5(3) Å3, and Z =8. The strongest seven lines in the X-ray powder diffraction pattern [d in Å (I/I0) (hkl)] are 2.982 (78) (400), 2.668 (100) (420), 2.435 (42) (510), 2.178 (20) (521), 1.935 (21) (611), 1.654 (20) (640), and 1.594 (30) (642). A momoiite solid solution substantially exists at relatively low pressure; however, extremely high momoiite content may not be formed in the pressure conditions of ore deposits in the Kurase, Hokkejino, and Fujii mines even if V and Mn are highly concentrated in the ore.
The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
- Vol.31 (1944) No. 5 and No.6 of the predecessor journal, "The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists" are available at this J-Stage site. (updated Aug. 2, 2018)