SECTOR GROWTH AND SYMMETRY OF (F,OH) APATITE FROM THE ASIO MINE, JAPAN

A study of apatite crystals from the Asio mine, Japan, showed sectoral texture related to the growth of the crystal, and with optically biax ial properties within the sectors. Wet chemical analysis gave a compos ition 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-ra y 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 pro duced during nonequilibrium crystal growth. The fluorine/hydroxyl site s in hexagonal apatite are symmetrically equivalent in the solid cryst al but, at a growth surface, this equivalence may be lost, resulting i n a reduction of crystal symmetry. Heating of the apatite to about 850 -degrees-C results in the almost complete disappearance of the optical anomalies due to disordering, which may be related to the loss of hyd roxyl from the crystal.