Abstract
Sibirskite was found in a vein consisting of borate minerals which developed along the boundary between crystalline limestone and skarns at Fuka, Okayama Prefecture, Japan. Sibirskite occurs as aggregates of prismatic crystals up to 0.1 mm long and 0.02mm wide, in association with takedaite, frolovite and calcite. Wet and microprobe analyses of sibirskite from Fuka give the empirical formula Ca1.004H1.071B0.974O3 on the basis of 0=3. The formula, optical properties and X-ray powder data are consistent with those from the type locality. The space group and cell dimensions determined are P21/a, a=8.643(6), b=9.523(2), c=3.567(3) Å, β=119.23(3)° and Z=4. The calculated density is 2.59 g cm−3, and agrees with the measured value of 2.58 g cm−3.
It is likely that sibirskite at Fuka was formed by late-hydrothermal alteration of takedaite.
