Ferri-fluoro-katophorite from Bear Lake diggings, Bancroft area, Ontario, Canada: a new species of amphibole, ideally Na(NaCa)(Mg4Fe3+)(Si7Al)O22F2

摘要

Ferri-fluoro-katophorite is the second species characterised involving the rootname katophorite in the sodium-calcium subgroup of the amphibole supergroup. The mineral and its name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2015-096. It was found in the Bear Lake diggings, Bancroft area, Ontario, Canada, where coarse euhedral crystals of amphibole, phlogopite, sanidine solid-solution (now coarsely exsolved to microcline perthite), titanite, augite, zircon and fluorapatite crystallised from a low-viscosity silicocarbonatitic magma of crustal origin. Greenish grey prismatic crystals of ferri-fluoro-katophorite generally protrude from the walls into a body of coarsely crystalline calcite, but they also occur away from the walls, completely enclosed by calcite. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: (A)(Na-0.55-K-0.32)(Sigma 0.87) (B)(Na0.79Ca1.18Mn0.032+)(Sigma 2.00) (C)(Mg(3.29)Mn(0.02)(2+)Fe(1.19)3+Al0.09Ti0.084+Li0.02)(Sigma 5.00)(T)(Si7.392Al0.61)(Sigma 8.00)O-22 (W)[F-1.23(OH)(0.77)](Sigma 2.00.) T(Ferri-fluoro-katophorite is biaxial (-), with alpha = 1.640(2), beta = 1.652(2), gamma = 1.658(2), 2V(meas). = 68.9(2)degrees and 2V(calc.). = 70.1 degrees. The unit-cell parameters are a = 9.887(3), b = 18.023(9), c = 5.292(2) angstrom, beta = 104.66(3)degrees, V = 912.3(6) angstrom(3), Z = 2 and space group C2/m. The strongest ten lines in the powder X-ray pattern [d values (in angstrom) I (hkl)] are: 2.708, 100, (151); 2388, 74, (131); 3.139, 72, (310); 8.449, 69, (110); 2.540, 65, ((2) over bar 02); 2.591, 53, (061); 2.739, 47, ((3) over bar 31); 2.165, 45, (261); 3.279, 44, ((2) over bar 40); 2.341, 43, ((3) over bar 51).