Kayupovaite, Na2Mn10[(Si14Al2)O38(OH)8]⋅7H2O – a new stilpnomelane-related mineral from the Ushkatyn-III deposit, Kazakhstan

Abstract

Kayupovaite, with the idealized formula Na₂Mn₁₀[(Si₁₄Al2)O₃₈(OH)₈]⋅7H₂O, is a new mineral named in honor of Maria Mikhailovna Kayupova (1921–1980), the mineralogist of the Satpaev Institute of Geological Sciences (Alma-Ata, USSR) who studied the Ushkatyn-III complex baryte–lead/iron–manganese deposit, Karagandy Province, Kazakhstan, the type of locality of the described mineral. Kayupovaite forms coarse lamellar (typically bent and split), light-gray, greasy luster crystals up to 0.2×0.15×0.01 mm in size, combined into radial, scaly, or lamellar aggregates up to 3×3×0.5 cm and embedded in a calcite–rhodonite matrix. Optically, in transmitted light, kayupovaite is colorless, with undulatory extinction due to the crystal curvature. It is non-pleochroic and biaxial (–), with α of 1.551(4) and β=γ1.586(2), 2Vmeas=3±1°. Kayupovaite is monoclinic and of space group C2/c, with a=24.9149(9), b=16.4343(5), c=22.3974(7) Å, β=94.408(3)°, V=9143.7(5) ų, and Z=8. The strongest lines of the powder X-ray diffraction pattern (d in Å (I) (hkl)) are as follows: 12.34(100)(200), 3.45(8)(71-1), 3.09(8)(800), 2.85(100)(121), 2.5946(12)(714), 2.642(11)(354), 2.614(7)(40-8), and 2.414(7)(554). The Raman spectrum of kayupovaite contains the following bands (cm⁻¹): 3635 and 3560 (O–H stretching vibrations of OH groups and H₂O molecules); 1041, 768, 742, and 717 (Si–O and Al–O stretching modes); 657, 532, 499, 460, 405, 374, and 333 (Mn–O stretching and Si–O–Si modes); and 304, 291, 224, 157, and 100 (lattice modes). The absorption bands of the infrared spectrum are as follows (cm⁻¹): 3629, 3511, and 3390 (O–H stretching vibrations of OH groups and H₂O molecules); 1640 (H₂O bending vibrations); 1020 (Si–O stretching vibrations); 778 (^IVAl–O stretching vibrations); 724 (Mn–O–H bending mode); 651 (O–Si–O bending mode); and 459 (Mn²⁺–O stretching vibrations). The empirical formula of kayupovaite, calculated on the basis of (O + OH) = 46 atoms per formula unit, is (Na_0.91K_0.46Ca_0.14)_Σ1.51(Mn9.292+Mg_0.89Zn_0.02)_Σ10.20[(Si_14.28Al_1.61)_Σ15.89O₃₈(OH)₈]⋅7.23H₂O. The mineral belongs to the group of modulated manganese phyllosilicates and is structurally related to stilpnomelane. The absence of iron in the mineral is a result of oxidative Mn–Fe fractionation during the formation of braunite-rich Mn ores.