Shimazakiite, Ca₂B_2-xO_5-3x(OH)_3x (x = 0 - 0.06), a new mineral from Fuka, Okayama Prefecture, Japan

Abstract

Shimazakiite occurs as grayish white aggregates up to 3 mm in diameter of tiny granular crystals in an irregular vein in crystalline limestone near gehlenite - supurrite skarns at Fuka, Okayama Prefecture, Japan. Associated minerals are takedaite, sibirskite, olshanskyite, parasibirskite, nifontovite, calcite and an undetermined hydrous calcium borate. It is Biaxial (-), α = 1.586(2), β = 1.650(2), γ = 1.667(2) (589 nm), 2V (calc.) = 53º. Electron microprobe analyses (WDS) gave an empirical formula; Ca₂B_1.94O_4.71(OH)_0.40. Electron diffraction patterns showed the minerals to be monoclinic with possible space groups of P2, P2/m, Pm, P21 or P21/m. The lattice parameters refined from IP-Gandolfi XRD data are; a = 3.532(3), b = 6.354(2), c = 19.275(9) Å, β = 91.30(8)º, V = 432.5(4) Å3, and Z = 4. The three strongest XRD lines [d in Å (I) hkl] are; 3.02 (84) 022, 2.92 (100) 112 and 2.81 (56) 11–3.