Okayamalite, Ca<sub>2</sub>B<sub>2</sub>SiO<sub>7</sub>, a new mineral, boron analogue of gehlenite

DOI Web Site 被引用文献5件

抄録

<jats:title>Abstract</jats:title><jats:p>Okayamalite, Ca<jats:sub>2</jats:sub>B<jats:sub>2</jats:sub>SiO<jats:sub>7</jats:sub>, tetragonal,<jats:italic>P</jats:italic><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" mime-subtype="png" xlink:href="S0026461X00012524_inline01.png" />21<jats:italic>m</jats:italic>,<jats:italic>a</jats:italic>= 7.116,<jats:italic>c</jats:italic>= 4.815 Å, Z = 2, is a new member of melilite group, the boron analogue of gehlenite. Electron microprobe analysis gave CaO 46.28, B<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>28.50, SiO<jats:sub>2</jats:sub>24.24, Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>0.36, total 99.38 wt.%, corresponding to Ca<jats:sub>2.01</jats:sub>B<jats:sub>2.00</jats:sub>Si<jats:sub>0.98</jats:sub>Al<jats:sub>0.02</jats:sub>O<jats:sub>7</jats:sub>, a natural counterpart of Ca<jats:sub>2</jats:sub>B<jats:sub>2</jats:sub>SiO<jats:sub>7</jats:sub>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 (<jats:italic>a</jats:italic>= 7.115, and<jats:italic>c</jats:italic>= 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/cm<jats:sup>3</jats:sup>. 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: CaCO<jats:sub>3</jats:sub>+ CaSiO<jats:sub>3</jats:sub>+ B<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>= Ca<jats:sub>2</jats:sub>B<jats:sub>2</jats:sub>SiO<jats:sub>7</jats:sub>+ CO<jats:sub>2</jats:sub>, arising from boron metasomatism of a wollastonite-calcite aggregate. The name is for the prefecture.</jats:p>

収録刊行物

被引用文献 (5)*注記

もっと見る

キーワード

詳細情報 詳細情報について

問題の指摘

ページトップへ