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Okayamalite, Ca2B2SiO7, a new mineral, boron analogue of gehlenite

Published online by Cambridge University Press:  05 July 2018

Satoshi Matsubara ,
Ritsuro Miyawaki ,
Akira Kato ,
Kazumi Yokoyama  and
Akiyoshi Okamoto
Satoshi Matsubara
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku, Tokyo 169, Japan
Ritsuro Miyawaki
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku, Tokyo 169, Japan
Akira Kato
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku, Tokyo 169, Japan
Kazumi Yokoyama
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku, Tokyo 169, Japan
Akiyoshi Okamoto
Affiliation:
3-11-5 Ooeda Minami Fukunishi-cho, Nishigyo, Kyoto 610-11, Japan
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Abstract

Okayamalite, Ca2B2SiO7, tetragonal, P21m, a = 7.116, c = 4.815 Å, Z = 2, is a new member of melilite group, the boron analogue of gehlenite. Electron microprobe analysis gave CaO 46.28, B2O3 28.50, SiO2 24.24, Al2O3 0.36, total 99.38 wt.%, corresponding to Ca2.01B2.00Si0.98Al0.02O7, a natural counterpart of Ca2B2SiO7 known only synthetically. The strongest lines in the X-ray powder diffraction pattern are 3.479 (40)(111), 2.862 (55)(201), 2.654 (100)(211), 2.129 (20)(301), 1.920 (35)(212), 1.644 (29)(312), very close to those of the synthetic material (a = 7.115, and c = 4.812 ). It is creamy white in colour with an earthy appearance due to the fine grain size. Streak white, cleavage not observed. Hardness ∼5½. Density calculated on the ideal formula is 3.30 g/cm3. It is optically uniaxial negative with ω = 1.700, and ɛ = 1.696. It occurs as patches of a few millimetres across in grey homogeneous-looking aggregate of wollastonite, vesuvianite, calcite and johnbaumite from Fuka mine, Bicchu-cho, Okayama Prefecture, Japan. The patches consist of very fine grains of the mineral up to 30 μm. Okayamalite is considered to be a product after the reaction formula: CaCO3 + CaSiO3 + B2O3 = Ca2B2SiO7 + CO2, arising from boron metasomatism of a wollastonite-calcite aggregate. The name is for the prefecture.

Keywords

okayamalitenew mineralmelilite groupborongehleniteX-ray dataelectron microprobe dataoptical dataFukaJapan
Type
Research Article
Information
Mineralogical Magazine , Volume 62 , Issue 5 , October 1998 , pp. 703 - 706
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

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References

Bauer, H. (1962) Über Diadochie zweischen Aluminium und Bor in Gehlenit. Neues Jahrb. Mineral. Mh., 127–40.Google Scholar
Fujiwara, T., Takada, M., Masutomi, K., Isobe, T., Okada, H., Nakai, I. and Nagashima, K. (1982) Pentahydroborite from Fuka, Okayama Prefecture, Japan. Chigaku Kenkyu (Geoscience Magazine), 33, 11–20. (in Japanese).Google Scholar
Grew, E.S. (1996) Borosilicates (exclusive of tourmaline) and boron in rock-forming minerals in metamorphic environments. In: Reviews in Mineralogy Vol. 33, (Grew, E.S. and Anovitz, L.M., eds.), Mineral. Soc. America, 387–502.Google Scholar
Henmi, K., Kusachi, I. and Numano, T. (1971) Contact minerals from Kushiro, Hiroshima Prefecture (1) Gehlenite and hydrogrossular. J. Mineral. Soc. Japan, 10, 160–9 (in Japanese).Google Scholar
Kusachi, I. , Henmi, C. and Kobayashi, S. (1995) Takedaite, a new mineral from Fuka, Okayama Prefecture, Japan. Mineral. Mag., 59, 549–52.CrossRefGoogle Scholar
Tarney, J., Nicol, A.W. and Marriner, G.F. (1973) The thermal transformation of datolite, CaBSiO4(OH), to boron-melilite. Mineral. Mag., 39, 158–75.CrossRefGoogle Scholar
Watanabe, T. (1939) Kotoit, ein neues gesteinbildendes Magnesiumborat. Tschermaks Mineral. Petrogr. Mitt., 50, 441–63.Google Scholar
Watanabe, T. (1943) Geology and mineralization of the Suian district, Tyosen (Korea). J. Fac. Sci. Hokkaido Univ., Ser. IV, 6, 205–303.Google Scholar
Watanabe, T. (1953) Suanite, a new magnesium borate mineral from Hol Kol, Suan, North Korea. Mineral. J., 1, 54–62.CrossRefGoogle Scholar
Watanabe, T., Kato, A. and Katsura, T. (1963) Kotoite, Mg3(BO3)2, from the Neichi Mine, Iwate Prefecture, Japan. Proc. Japan Acad., 39, 164–9.CrossRefGoogle Scholar