IMA 2016–015 = arsenatrotitanite

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Marco E. Ciriotti
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IMA 2016–015 = arsenatrotitanite

Messaggio da Marco E. Ciriotti » gio 05 lug, 2018 10:25

Prossima pubblicazione.

▪ Pekov, I.V., Zubkova, N.V., Agakhanov, A.A., Belakovskiy, D.I., Vigasina, M.F., Yapaskurt, V.O., Sidorov, E.G., Britvin, S.N., Pushcharovsky, D.Y. (2018): New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. IX. Arsenatrotitanite, NaTiO(AsO4). Mineralogical Magazine, 82, (in press).

The new durangite-group mineral arsenatrotitanite, ideally NaTiO(AsO4), was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with orthoclase, tenorite, hematite, johillerite, bradaczekite, badalovite, calciojohillerite, arsmirandite, tilasite, svabite, cassiterite, pseudobrookite, rutile, sylvite, halite, aphthitalite, langbeinite, and anhydrite. Arsenatrotitanite occurs as prismatic, tabular, lamellar or acicular crystals up to 0.3 × 0.8 × 2 mm. They are separated or combined in open-work aggregates up to 2-mm across or interrupted crusts up to 2 x 5 mm2 in area and up to 0.3 mm thick. Arsenatrotitanite is transparent, brownish red to pale pinkish-reddish or almost colourless, with vitreous lustre. It is brittle, the Mohs’ hardness is ca 5½. Cleavage is perfect on (110), the fracture is stepped. Dcalc is 3.950 g cm-3. Arsenatrotitanite is optically biaxial (+), α = 1.825(5), β = 1.847(6), γ = 1.896(6) (589 nm), 2Vmeas = 70(5)º. Chemical composition (wt%, electron-microprobe) is: Na2O 12.26, CaO 3.10, Al2O3 4.39, Fe2O3 9.57, TiO2 17.11, SnO2 1.03, As2O5 50.17, F 3.29, O = F –2.39, total 99.53. The empirical formula based on 5 (O+F) apfu is (Na0.91Ca0.13)Σ1.04(Ti0.49Fe3+0.27Al0.20Sn0.02)Σ0.98(As1.00O4.00)(O0.60F0.40). Arsenatrotitanite is monoclinic, C2/c, a = 6.6979(3), b = 8.7630(3), c = 7.1976(3) Å, β = 114.805(5)º, V = 383.48(3) Å3 and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 4.845(89)(-111), 3.631(36)(021), 3.431(48)(111), 3.300(100)(-112), 3.036(100)(200), 2.627(91)(130) and 2.615(57)(022). The crystal structure was solved from single-crystal XRD data, R = 1.76%. Arsenatrotitanite belongs to the titanite/durangite structure type. It is named as an arsenate of sodium (natrium in Latin) and titanium isostructural with titanite.
Marco E. Ciriotti

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