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Sector growth and symmetry of (F,OH) apatite from the Asio mine, Japan

Published online by Cambridge University Press:  05 July 2018

Mizuhiko Akizuki
Affiliation:
Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Tohoku University, Sendai 980, Japan
Hirotugu Nisidoh
Affiliation:
Hiruzen Research Institute, Okayama University of Science, Kamifukuda, Maniwa-Gun, Okayama 717-06, Japan
Yasuhiro Kudoh
Affiliation:
Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Tohoku University, Sendai 980, Japan
Tomohiro Watanabe
Affiliation:
Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Tohoku University, Sendai 980, Japan
Kazuo Kurata
Affiliation:
Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Tohoku University, Sendai 980, Japan

Abstract

A study of apatite crystals from the Asio mine, Japan, showed sectoral texture related to the growth of the crystal, and with optically biaxial properties within the sectors. Wet chemical analysis gave a composition Ca5(PO4)3(F0.64,OH0.38,Cl0.01)1.03 for the specimen.

Additional diffraction spots were not observed in precession and oscillation X-ray photographs and electron diffraction photographs. Since the internal textures correlate with the surface growth features, it is suggested that the internal textures and the unusual optical properties were produced during nonequilibrium crystal growth. The fluorine/hydroxyl sites in hexagonal apatite are symmetrically equivalent in the solid crystal but, at a growth surface, this equivalence may be lost, resulting in a reduction of crystal symmetry. Heating of the apatite to about 850°C results in the almost complete disappearance of the optical anomalies due to disordering, which may be related to the loss of hydroxyl from the crystal.

Type
Mineralogy
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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