Kreiterite, CsLi₂Fe⁺³(Si₄O₁₀)F₂, a New Cesium Mica from the Darai-Pioz Alkaline Massif, Tajikistan

Kreiterite, CsLi₂Fe⁺³(Si₄O₁₀)F₂, a new cesium trioctahedral mica was discovered in the Darai-Pioz alkaline massif (Tajikistan). It is named after the Russian geologist, Prof. Vladimir Mikhailovich Kreiter (1897–1966). Kreiterite occurs as lamellar grains or flakes up to 0.2 mm across, irregular in shape and usually slightly deformed, in quartz-pectolite aggregates within so-called “quartz lumps”, the rocks consisting mainly of granular quartz. The mineral is colorless and transparent with vitreous luster. Mohs hardness is 2½, D_meas. is 3.33(2) g/cm³, and D_calc. is 3.342 g/cm³. The new mineral is optically biaxial (−) with α = 1.596(2), β = 1.605(2), γ = 1.607(2), 2V(calc) = −50°. It is monoclinic, space group C2/m, C2, or Cm (polytype 1M), a = 5.240(2) Å, b = 9.054(4) Å, c = 10.767(4) Å, β = 99.58(4)°, V = 503.4(6) ų, and Z = 2. The strongest lines in the powder diffraction pattern are (d Å, I %, hkl): 4.49, 31, (1 1 0); 3.94, 31, (1 1 1); 3.70, 47, (⁠ 1 2), (⁠ 2); 3.45, 36, (0 2 2); 3.00, 34, (⁠ 1 ⁠), (⁠ 3); 2.652, 17, (0 0 4); 2.610, 72, (⁠ 0 1), (1 3 0), (⁠ 3 0); 2.583, 100, (2 0 0), (⁠ 3 1); 2.241, 38, (2 2 0); 2.190, 67, (⁠ 3 3). Chemical analysis by electron microprobe and SIMS (for H₂O and Li₂O) gave SiO₂ 47.37, TiO₂ 0.99, Al₂O₃ 0.29, MgO 0.40, Fe₂O₃ 13.18, ZnO 0.12, K₂O 0.02, Cs₂O 27.37, Li₂O 5.90, H₂O 1.28, F 4.77, −O=F −2.01, total 99.68 wt.% The empirical formula, based on 12 (O+F), is Cs_0.99Li_2.01(Fe³⁺_0.84Ti_0.06Mg_0.05Al_0.03Zn_0.01)_Σ0.99Si_4.01O₁₀(F_1.28OH_0.72)_Σ2. Kreiterite is a ferric-iron analogue of sokolovaite and gorbunovite and the lithium ferric-iron analogue of garmite.