滋賀県甲西町花園産花こう岩ペグマタイト中のアルカリ長石

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タイトル別名
  • シガケン コウセイチョウ ハナゾノサン カコウガン ペグマタイトチュウ ノ ア
  • シガケン コウセイチョウ ハナゾノサン カコウガン ペグマタイトチュウ ノ アルカリ チョウセキ
  • Alkali Feldspar in Granite Pegmatite from Hanazono, Kosei Town, Shiga Prefecture, Japan

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type:Departmental Bulletin Paper

Alkali feldspar (Or66Ab33An0.6) in granite pegmatite from Hanazono, Kosei Town, Shigaprefecture, Japan, consists of two parts macroscopically (with the naked eye); one is noncolored and transparent, and another is pinkish and opaque. The latter part ranging from several milimeters to about one centimeter is scattered in the dominant former part. The two parts are microscopically mixed up irregularly in a micron-order, too. The transparent part is clear, and cryptoperthitic of braid-type or lamellar type, or featureless without microtextute, and the pinkish part is turbid and microperthitic of vein-type under an optical microscope. Both the microperthite and braid-cryptoperthite were examined with EPMA, and the size, form and orientation of lamellae or vein, distribution of micropores in both the clear and turbid parts, and compositional variation patterns in microperthitc Ab-rich veins were clrified. The textural features of the alkali feldspar are principally similar to those of the Klokken syenite feldspars. The Klokken model of feldspar cooling, which advocates deuteric coarsening of cryptoperthite to microperthite with micropore formation at the hydrothermal stage in plutonic rocks, may be appllicable to the Hanazono alkali feldspar, in spite of the difference of their bulk compositions. Irregular and complicated Ca distribution patterns in the Hanazono Ab-rich veins, however, throw new insight to the Klokken cooling model.

identifier:滋賀大学教育学部紀要, 3, 自然科学, 第47号, pp.25-39

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