IMA 2015-096 = ferri-fluoro-katophorite

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Marco E. Ciriotti
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IMA 2015-096 = ferri-fluoro-katophorite

Messaggio da Marco E. Ciriotti » mer 04 lug, 2018 10:26

Prossima pubblicazione.

Referenza:
▪ Oberti, R., Boiocchi, M., Hawthorne, F.C., Ball, N.A., Martin, R.F. (2018): Ferri-fluoro-katophorite from Bear Lake diggings, Bancroft area, Ontario, Canada: a new species of amphibole, ideally Na(NaCa)(Mg4Fe3+)(Si7Al)O22F2. Mineralogical Magazine, 82, (in press).

Abstract:
Ferri-fluoro-katophorite is the second species characterised involving the rootname katophorite in the sodium-calcium subgroup of the amphiboles. The mineral and its name were approved by the IMA-CNMNC, vote 2015-096. 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 crystallized 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(Na0.55K0.32)Σ=0.87 B(Na0.79Ca1.18 Mn2+0.03)Σ=2.00 (Mg3.29Mn2+0.02 Fe2+1.19Fe3+0.31Al0.09Ti4+0.08Li0.02)Σ=5.00 T(Si7.39Al0.61)Σ=8.00 O22 W[F1.23 (OH)0.77]Σ=2.00. Ferri-fluoro-katophorite is biaxial (-), with α = 1.640(2), β = 1.652(2), γ = 1.658(2) and 2V (meas.) = 68.9(2)º, 2V (calc.) = 70.1º. The unit-cell parameters are a = 9.887(3), b = 18.023(9), c = 5.292(2) Å, β = 104.66(3)°, V = 912.3 (6) Å3, Z = 2, space group C2/m. The strongest ten reflections in the X-ray powder 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, (-202); 2.591, 53, (061); 2.739, 47, (-331); 2.165, 45, (261); 3.279, 44, (-240); 2.341, 43, (-351).
Marco E. Ciriotti

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