Kôzulite, an Mn-rich alkali amphibole

The crystal structure of kôzulite, an Mn-rich alkali amphibole with the ideal formula NaNa(2)[Mn(4) (2+)(Fe(3+),Al)]Si(8)O(22)(OH)(2), tris­odium tetra­manganese iron/aluminium octa­silicate dihydroxide, was refined from a natural specimen with composition (K(0.20)Na(0.80))(Na(1.60)Ca(0.18)Mn(2+) (0.22))(Mn(2+) (2.14)Mn(3+) (0.25)Mg(2.20)Fe(3+) (0.27)Al(0.14))(Si(7.92)Al(0.06)Ti(0.02))O(22)[(OH)(1.86)F(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 Mn(2+) 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.