Vimsite from the Fuka mine, Okayama Prefecture, Japan

Vimsite was found as a mass or a veinlet in crystalline limestone associated with gehlenite-spurrite skarns at the Fuka mine, Okayama Prefecture, Japan. Vimsite occurs as colorless to white aggregates of anhedral or prismatic transparent crystals up to 1 mm in length in association with shimazakiite, sibirskite, priceite, uralborite, calciborite, kurchatovite, and calcite. It is also formed as a 0.5 mm wide veinlet. An electron microprobe analysis of vimsite gave an empirical formula (Ca0.993Mg0.009Fe0.003Mn0.001)(Sigma 1.006)B1.996O2(OH)(4) based on O = 6. The unit cell parameters are a= 10.021(3), b = 9.566(4), c = 4.447(2) angstrom, beta= 91.231 (9)degrees. The calculated density is 2.523 g cm(-3). TheVickers microhardness is 186-206 kg mm(-2) (25 g load). It is likely that vimsite from the Fuka mine was formed by subsequent hydrothermal alteration, as with uralborite and priceite, of sibirskite produced by the hydrothermal alteration of shimazakiite.