Crystal structure and chemical composition of Li-, Fe-, and Mn-rich micas

Abstract

The crystal chemistry of three Li-, Fe-, and Mn-rich trioctahedral micas has been characterized by single-crystal X-ray diffraction. The samples are from Hirukawa mine, Japan: (Si_3.43Al_0.57)(Al_1.00 Fe_0.38Mg_0.01Mn_0.17Li_1.44)(Na_0.05K_0.95)O₁₀F_1.88(OH)_0.12; from Mokrusha mine, Russia: (Si_3.30Al_0.70)(Al_1.00Fe_0.36 Mg_0.01Mn_0.31Li_1.32)(Ca_0.01Na_0.04K_0.94)O₁₀F_1.91(OH)_0.09; and from Sawtooth Mountains, Boise County, Idaho, U.S.A.: (Si_3.11Al_0.89)(Al_0.91Ti_0.02Fe_0.46Mg_0.03Mn_0.52Li_1.06)(Na_0.05K_0.92Rb_0.02)O₁₀F_1.89(OH)_0.11. Our crystals belong to the 1M polytype with layer symmetry C121(1) and show M1 and M3 sites much larger in size than M2. Mean electron-count (m.e.c.) values are more variable for the M1 and M3 sites than for M2. With the exception of the sample from Sawtooth Mountains, all tetrahedral mean bond lengths appear to be smaller for T1 than for T11 site. When compared to the Li- and Fe-rich series, crystals show similar crystal-chemical trends, thus suggesting that the layer structure is affected in a similar way by Fe and Mn cations