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Minyulite is a rare phosphate mineral with a chemical formula of KAl2(OH,F)(PO4)2·4(H2O).〔 It occurs as groups of radiating fine fibrous crystals within rock cracks of phosphatic ironstone. Minyulite belongs to the orthorhombic crystal system. This indicates that it has three axes of unequal length yet all are perpendicular to each other. It's cell constants are a=9.35, b=9.74 c=5.52. 〔Kampf, A.R. (1977) Minyulite: its atomic arrangement. American Mineralogist, 62, 256–262. 〕 As for its optical properties, Minyulite is an anisotropic mineral which means the velocity of light differs when traveling through it depending on the cut of its cross section which gives it more than one refractive index. 〔Klein, C., and Dutrow, B.(2007) The 23rd Edition of the Manual of Mineral Science, 290 p. John Wiley and Sons, Inc. Hoboken, New Jersey,U.S.A. 〕 The mineral is optically biaxial. Its birefringence value is 0.007.〔Spencer, L.J., F.A. Bannister, M.H. Hey, and H. Bennett (1943) Minyulite (hydrous K-Al fluophosphate) from South Australia. Mineralogical Magazine, 26, 309–314.〕 It has three refractive indices which are nα=1.531 nβ=1.534 nγ=1.538. 〔Simpson, E.S., and Le Mesurier, C.R.(1933)Minyulite: a new phosphate mineral from Dandaragn. Journal of the Royal Society of Western Australia: 19-13.〕 Refractive indices are a ratio of the speed of light in a median with respect to the speed of light passing through the mineral.〔 ==Occurrence== It was first described in 1933 for an occurrence in Western Australia and named after the type locality, Minyulo Well in Western Australia.〔 Minyulite is considered as a secondary phosphate since it is formed by the alteration of a primary phosphate. It occurs in association with dufrenite, apatite, fluellite, wavellite, variscite and leucophosphite.〔 The mineral can be found in the underlying phosphatized rock zone of ornithogenic soil. Minyulite is not found in abundance, it can be found in the sea shore of the maritime Arctic.〔 Tatur, A., and Keck, A. (1990) Phosphates in ornithogenic soils of the Maritime Antarctic.Proc. NIPR Symp. Polar Biol: 3, 133-150.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Minyulite」の詳細全文を読む スポンサード リンク
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