Kzulite, an Mn-rich alkali amphibole

The crystal structure of kôzulite, an Mn-rich alkali amphibole with the ideal formula NaNa₂[Mn₄ ²⁺(Fe ³⁺,Al)]Si₈O₂₂(OH)₂, tris-odium tetra-manganese iron/aluminium octa-silicate dihydroxide, was refined from a natural specimen with composition (K_0.20Na_0.80)(Na _1.60Ca_0.18Mn²⁺ _0.22)(Mn²⁺ _2.14Mn³⁺ _0.25Mg_2.20Fe³⁺ _0.27Al_0.14)(Si_7.92Al_0.06Ti _0.02)O₂₂[(OH)_1.86F_0.14]. The site occupancies determined from the refinements are M1 = 0.453 (1) Mn + 0.547 (1) Mg, M2 = 0.766 (1) Mn + 0.234 (1) Mg, and M3 = 0.257 (1) Mn + 0.743 (1) Mg, where Mn and Mg represent (Mn+Fe) and (Mg+Al), respectively. The average M - O bond lengths are 2.064 (1), 2.139 (1), and 2.060 (1) Å for the M1, M2, and M3 sites, respectively, indicating the preference of large Mn²⁺ for the M2 site. Four partially occupied amphibole A sites were revealed from the refinement, with A(m) = 0.101 (4) K, A(m)′ = 0.187 (14) Na, A(2) = 0.073 (6) Na, and A(1) = 0.056 (18) Na, in accord with the result derived from microprobe analysis (0.20 K + 0.80 Na), considering experimental uncertainties.