Presentation Information
[R1P-09]Proto-ferro-anthophyllite in a granitic pegmatite from Nomi Island, Hiroshima Prefecture, Japan
*Masayuki Ohnishi1, Norimasa Shimobayashi2, Daisuke Nishio-Hamane3, Shinoda Keiji4, Satomi Enju5 (1. Non, 2. Kyoto Univ., 3. ISSP, Univ. of Tokyo, 4. Osaka Metro. Univ., 5. Ehime Univ.)
Keywords:
Proto-ferro-anthophyllite,Amphibole,Granitic pegmatite,Nomi Island,Etajima
Proto-ferro-anthophyllite was found in a granitic pegmatite from Nomi Island (Ogaki-cho Okimi, Etajima City), Hiroshima Prefecture, Japan. The mineral occurs as fibrous crystals up to 4 mm in length, in association with fayalite, magnetite, “biotite”, and quartz. It is white to colorless or pale brown, transparent with a vitreous luster. The refractive indices are α = 1.670(3), β = n.d., and γ = 1.704(3). SEM-EDS analyses gave the empirical formula ((Vacancy)0.89Na0.10K0.01)Σ1.00(Fe6.24Mg0.41Mn0.36Ca0.02Cr0.01Ti0.01)Σ7.05(Si7.90Al0.10)Σ8.00O22(OH)2 on the basis of O = 22 (anhydrous part). Selected area electron diffraction pattern indicated the Pnmn structure type. The unit cell parameters calculated from powder X-ray diffraction data are a = 9.43(3), b = 18.14(3), and c = 5.34(1) Å. It is likely that proto-ferro-anthophyllite from Nomi Island was formed by a late-hydrothermal alteration of fayalite.
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