Borcarite from Fuka, Okayama Prefecture, Japan

摘要

Borcarite was found in a vein cavity which developed along the boundary between crystalline limestone and gehlenite-spurrite skarns at Fuka, Okayama Prefecture, Japan. Borcarite occurs as scattered prismatic intergrowths and euhedral crystals up to 5 mm long and 3 mm wide on the cavity wall, in association with olshanskyite, bultfonteinite and calcite. Wet chemical analyses and EPMA of the mineral yield an empirical formula Ca_(3.944)(Mg_(0.815) Fe_(0.089))_(Σ0.904)B_(3.981)O_(5.705)(OH)_(6.097)(CO_3)_(2.066) on the basis of O = 18. The DTA and TG curves, IR spectrum and X-ray diffraction properties agree well with previous data. It is likely that borcarite was formed as a secondary mineral from brucite in a reaction with late-hydrothermal solution.