Potassic-aluminotaramite from Sierra de los Filabres, Spain

Potassic-aluminotaramite, ideally ^AK (CaNa)^B (Fe²₃⁺Al₂)^C (Si₆Al₂) O₂₂^W (OH)₂, has been found in a meta-monzonite rock sampled at Sierra de los Filabres, S.E. Spain; the paragenesis that contains the amphibole is mainly formed by feldspar, quartz, and clinopyroxene. This paper reports a complete mineral description and crystal-structure details for this new taramite end-member that has been recognised by IMA-CNMMC with the vote 2007-015. Holotype potassic-aluminotaramite has the experimental unit formula ^A(Na_0.34K_0.66)_∑1.00 ^B(Fe²⁺_0.01Na_0.85 Ca_1.14)_∑2.00^C (Fe²⁺_2.80Mg_0.33Al_1.26 Fe³⁺_0.46Ti_0.05 Mn_0.10)^T_∑5.10(Si_6.01 Al_1.99)_∑8.00O₂₂^W (OH_1.96F_0.03Cl_0.01) _∑2.00; a = 9.8505(5), b = 18.0075(9), c = 5.3518(3) Å β = 104.775(4), V = 917.9(2) ų; D_calc = 3.40 g/cm³. Optics: biaxial (-); α 1.686(1), β 1.703(3), γ 1.706(3) (λ = 589 nm). The ten strongest reflections in the X-ray powder pattern [d values (in Å), I, (hkl)] are: 8.420, 100, (110); 2.714, 75.03, (151); 2.565, 59.62, (-202); 3.127, 52.54, (310); 2.596, 49.03, (061); 3.400, 37.92, [(131) (041)]; 2.166, 33.71, [(261) (-332)]; 2.340, 32.38, (-351); 2.956, 24.79, (221); 2.297, 24.57, [(-171) (-312)].