Borcarite from Fuka, Okayama Prefecture, Japan

Abstract

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)_Σ0.904B_3.981O_5.705(OH)_6.097(CO₃)_2.066 on me 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.