Abstract
Potassicleakeite, KNa2Mg2Fe3+2LiSi8O22(OH)2, the K-dominant leakeite, is found in manganese ore deposit at the Tanohata mine, Iwate Prefecture, Japan. It is monoclinic, C2/m, a = 9.922(5), b = 17.987(7), c = 5.286(2) Å, β = 104.07(3)°, V = 915.1(7) Å3 and Z = 2. The seven strongest lines in the X-ray powder diffraction pattern are 8.48(67)(110), 4.50(89)(040), 3.40(46)(131), 3.28(45)(240), 3.16(72)(310, 201), 2.83(49)(330), 2.53(100)(-202). Electron microprobe and LAM-ICP-MS analyses gave SiO2 55.34, TiO2 0.29, Al2O3 0.44, V2O3 5.52, Fe2O3 9.45, MnO 7.81, MgO 7.23, CaO 0.13, K2O 3.10, Na2O 8.73, Li2O 1.2, H2O (calc) 2.08, total 100.12 wt. %, corresponding to (K0.57Na0.46)Σ1.03(Na1.98Ca0.02)Σ2.00(Mg1.29Mn0.65)Σ1.94(Fe3+1.02V0.64Mg0.26Al0.05Ti0.03)Σ2.00-(Li0.70Mn0.30)Σ1.00(Si7.98Al0.02)Σ8.00O22(OH)2 on the basis of O + OH = 24. It is transparent and reddish brown with vitreous luster. The streak is pale brownish yellow and cleavage {110} is perfect. The fracture is uneven and tenacity is brittle. The hardness is VHN100 425 - 572 kg/mm2 (Mohs ∼5). The calculated density is 3.18 g/cm3. It is distinctly pleochroic from yellowish brown to reddish brown. It is optically biaxial positive with α = 1.672(2), β = 1.680(2), γ = 1.692(2), 2V(calc) = 79°, and orientation: b = Z, X^c = +35 to 40°. It occurs as prismatic crystals in veinlets composed mainly of quartz, alkali-feldspars, and serandite. The mineral is considered to be formed under the later stage of hydrothermal activities of contact metasomatism.
