2017 Volume 112 Issue 4 Pages 159-165
Kurchatovite occurs as colorless granular crystals up to 1 mm at the Fuka mine, Okayama Prefecture, Japan. The mineral is associated with shimazakiite, calcite and johnbaumite. The Vickers microhardness is 441 kg mm−2 (50 g load), corresponding to 4½ on the Mohs’ scale. The calculated density is 3.23 g cm−3. Electron microprobe analyses of kurchatovite gave empirical formulae ranging from Ca0.987(Mg1.004Fe0.020Mn0.001)Σ1.025B1.992O5 to Ca0.992(Mg0.466Fe0.523)Σ0.989B2.013O5 based on O = 5, and kurchatovite forms a continuous solid solution in this range. The mineral is orthorhombic, Pbca, and the unit cell parameters refined from XRD data measured by a Gandolfi camera are a = 36.33(14), b = 11.204(3), c = 5.502(17) Å, V = 2239(12) Å3. It is formed by a layer of MgO6–octahedra, a layer of CaO7–polyhedral and B2O5 consisting of two BO3–triangles. The kurchatovite from the Fuka mine was probably formed by supplying Mg and Fe to shimazakiite from hydrothermal solution at a temperature between 250 to 400 °C.