Katophorite from the Jade Mine Tract, Myanmar: mineral description of a rare (grandfathered) endmember of the amphibole supergroup

摘要

Katophorite has the ideal formula Na-A(B)(NaCa)(C)(Mg4Al)(T)(Si7Al)O-22(W)(OH)(2) (Hawthorne et al., 2012). No published analyses of amphiboles fall in the katophorite compositional field, except that of Harlow and Olds (1987) for an amphibole from near Hpakan in the Jade Mine Tract, Myanmar. This amphibole was approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (vote 2013-140) as katophorite, and is reported here. Holotype katophorite is monoclinic, space group C2/m, a = 9.8573(8), b = 17.9617(15), c = 5.2833(4) angstrom, b = 104.707(2)degrees, V = 904.78(13) angstrom(3), Z = 2. The calculated density is 3.091 g cm(-3). In plane-polarized light, katophorite is pleochroic, X = pale blue (medium), Y = light blue-green (strongest), Z = colourless; X boolean AND a = 30.6 degrees (beta obtuse), Y parallel to b, Z boolean AND c = 15.8 (beta acute). It is biaxial negative, alpha = 1.638, beta = 1.642, gamma = 1.644, all +/- 0.002; 2V(obs) = 73(1)degrees, 2V(calc) = 70 degrees. The eight strongest lines in the powder X-ray diffraction pattern are [d in angstrom (I)(hkl)]: 2.700 (100)(151), 3.129 (69)(310), 2.536 (65)((2) over bar 02), 3.378 (61)(131), 8.421 (55)(110), 2.583 (46)(061), 2.942 (43)(221) and 2.334 (41)((3) over bar 51). Electron-microprobe analysis of the refined crystal gave SiO2 51.74, Al2O3 7.38, TiO2 0.14, FeO 1.55, Fe2O3 2.82, MgO 18.09, CaO 8.17, Na2O 6.02, K2O 0.24, F 0.06, H2Ocalc. 1.80, Li2Ocalc. 0.09, sum 100.55 wt.% (Li2O and H2O based on the results of single-crystal structure refinement). The formula unit, calculated on the basis of 24 (O,OH,F) with (OH + F + O) = 2 is: (A)(Na0.85K0.04)(Sigma=0.89)(B)(Ca1.22Na0.78)(Sigma=2.00)(C)(Mg3.76Al0.43Fe0.303+Cr0.273+Fe0.182+Li0.05Ti0.014+)(Sigma=5.00)(T)(Si7.21Al0.79)(Sigma=8.00)O-22(W)[(OH)(1.67)O0.30F0.03)](Sigma=2.00).