Indialite from Unazuki Pelitic Schist,Japan, and its transition texture to cordierite |
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| Authors: | Masao Kitamura Yoshikuni Hiroi |
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| Institution: | (1) Department of Geology and Mineralogy, Faculty of Science, Kyoto University, Sakyo, 606 Kyoto, Japan;(2) Institute of Earth Science, Faculty of Education, Kanazawa University, 920 Kanazawa, Japan |
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| Abstract: | Indialite (hexagonal cordierite) has been found in a cordierite vein of polymetamorphosed pelitic rock, a member of the Unazuki
schists in Hida terrane, central Japan. Most of the indialite grains show intergrowth textures with cordierite of orthorhombic
symmetry. This is the second identification of indialite since the first one from a fused sediment in India.
The intergrowth texture was formed by a nucleation-growth process accompanied with the first order transition from the hexagonal
to the orthorhombic form. Characteristic pseudo-twin relation exists among the orthorhombic phases. Chemical compositions
of both hexagonal and orthorhombic forms in the intergrowth have been deter-mined by analytical electron microscopy. The difference
in Fe/(Mg+Fe) at the interfaces between the two forms indicates the existence of a transition loop in the (Mg, Fe)-cordierite.
The transition of the present specimens is estimated to have initiated at about 700° C. A possible phase diagram of (Mg, Fe)-cordierite
has been proposed, based on the result of this investigation. |
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