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

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: (Na0.55K0.32)?0.87(Na0.79Ca1.18Mn0.03)?2.00(Mg3.29Mn0.02Fe1.19Fe0.31Al0.09Ti0.08Li0.02)?5.00(Si7.39Al0.61)?8.00O22[F1.23 (OH)0.77]?2.00. Ferri-fluoro-katophorite is biaxial (-), with ? = 1.640(2), ? = 1.652(2), ? = 1.658(2), 2Vmeas. = 68.9(2)° and 2Vcalc.. = 70.1°. The unit-cell parameters are a = 9.887(3), b = 18.023(9), c = 5.292(2) Å, ? = 104.66(3)°, V = 912.3(6) Å, Z = 2 and space group C2/m. The strongest ten lines in the powder X-ray pattern [d values (in Å) I (hkl)] are: 2.708, 100, (151); 2.388, 74, (131); 3.139, 72, (310); 8.449, 69, (110); 2.540, 65, (02); 2.591, 53, (061); 2.739, 47, (31); 2.165, 45, (261); 3.279, 44, (40); 2.341, 43, (51).