Magnesio-riebeckite from Varenche mine (Aosta Valley): crystal-chemical characterization of a grandfathered end-member

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Marco E. Ciriotti
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Magnesio-riebeckite from Varenche mine (Aosta Valley): crystal-chemical characterization of a grandfathered end-member

Messaggio da Marco E. Ciriotti » lun 03 apr, 2017 10:41

Prossima pubblicazione.

Referenza:
▪ Oberti, R., Boiocchi, M., Hawthorne, F.C., Ciriotti, M.E. (2017): Magnesio-riebeckite from the Varenche mine (Aosta Valley, Italy): crystal-chemical characterization of a grandfathered end-member. Mineralogical Magazine, 81, (in press).

Abstract:
Magnesio-riebeckite from the dumps of the abandoned mine of Varenche (45°47'22'' N, 7°29'17''E), Saint-Barthélemy, Nus, Aosta Valley (Italy), was studied to provide the complete mineral description (included crystal structure) and insights into the crystal-chemistry of riebeckite. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is A(Na0.09K0.01)Σ=0.10 B(Na1.77Ca0.11Mg0.08Mn2+0.04)Σ=2.00 C(Mg2.93Mn2+0.13Fe2+0.07Zn0.01Ni0.12Fe3+1.25Al0.48Ti0.01)Σ=5.00 T(Si7.92Al0.08)Σ=8.00 O22 W(OH1.88F0.12)Σ=2.00. Magnesio-riebeckite is biaxial (+), with α = 1.678(2), β = 1.682(2), γ = 1.688(2) and 2V (meas.) = 80.2(1.7)º, 2V (calc.) = 78.7o. The unit-cell parameters are a = 9.6481(14), b = 17.873(3), c = 5.3013(7) Å, β = 103.630(2)°, V = 888.4 (2) Å3, Z = 2, space group C2/m. The strongest ten reflections in the X-ray powder pattern [d values (in Å), I, (hkl)] are: 2.701, 100, (151); 8.303, 83, (110); 3.079, 62, (310); 3.391, 53, (131); 4.467, 50, (040,021); 2.522, 50, (-202); 2.578, 35, (061); 2.155, 30, (261), 4.855, 30, (-111), 2.300, 29, (-351).
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Re: Magnesio-riebeckite from Varenche mine (Aosta Valley): crystal-chemical characterization of a grandfathered end-memb

Messaggio da TOSATO FABIO » lun 03 apr, 2017 20:25

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