Uralborite from Fuka, Okayama Prefecture, Japan 草地 功 白神 加奈子 小林 祥一 山川 純次 武智 泰史 日本鉱物科学会 Journal of mineralogical and petrological sciences 13456296 95 4 43 47 2000-04-01 Uralborite, CaB2O2(OH)4, was found in a vein consisting of borate minerals that cut into crystalline limestone at Fuka, Okayama Prefecture, Japan. It occurs as aggregates of fibrous crystals up to 0.2 mm long and as euhedral crystals up to 7 mm long and 3 mm wide, in association with sibirskite, borcarite, fluorite and calcite.    Electron microprobe analyses and ICP gave the empirical formula Ca1.006B2.019O2.069(OH)3.931 on the basis of O=6. X-ray powder diffraction were indexed on the monoclinic cell, a=6.923(1), b=12.326(1), c=9.831(1)Å, β=97.09(1)°, determined by a single crystal method. The mineral was optically biaxial positive with refractive indices α=1.605(2), β=1.611(2), γ=1.618(2). The Vickers microhardness was 372 kg mm−2 and the Mohs scale of hardness was 4.5. The density was 2.58(2) g cm−1. It is likely that uralborite at Fuka was formed as a secondary mineral by a late-hydrothermal alteration of sibirskite. 2000-04-01 10011128862 AA11460926 ENG CJP CJPref J-STAGE 0 11 2 Uralborite from Fuka, Okayama Prefecture, Japan KUSACHI Isao SHIRAGA Kanako KOBAYASHI Shoicih YAMAKAWA Junji TAKECHI Yasushi Japan Association of Mineralogical Sciences Journal of Mineralogical and Petrological Sciences Uralborite, CaB2O2(OH)4, was found in a vein consisting of borate minerals that cut into crystalline limestone at Fuka, Okayama Prefecture, Japan. It occurs as aggregates of fibrous crystals up to 0.2 mm long and as euhedral crystals up to 7 mm long and 3 mm wide, in association with sibirskite, borcarite, fluorite and calcite.    Electron microprobe analyses and ICP gave the empirical formula Ca1.006B2.019O2.069(OH)3.931 on the basis of O=6. X-ray powder diffraction were indexed on the monoclinic cell, a=6.923(1), b=12.326(1), c=9.831(1)Å, β=97.09(1)°, determined by a single crystal method. The mineral was optically biaxial positive with refractive indices α=1.605(2), β=1.611(2), γ=1.618(2). The Vickers microhardness was 372 kg mm−2 and the Mohs scale of hardness was 4.5. The density was 2.58(2) g cm−1. It is likely that uralborite at Fuka was formed as a secondary mineral by a late-hydrothermal alteration of sibirskite. 草地 功 KUSACHI Isao Department of Earth Sciences, Faculty of Education, Okayama University 白神 加奈子 SHIRAGA Kanako Department of Earth Sciences, Faculty of Education, Okayama University 小林 祥一 KOBAYASHI Shoicih Division of Earth Sciences, Kurashiki University of Science and the Arts 山川 純次 YAMAKAWA Junji Department of Earth Science, Faculty of Sciences, Okayama University 武智 泰史 TAKECHI Yasushi Kurashiki Museum of Natural History