IMA 2018-008 = zubkovaite

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Marco E. Ciriotti
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IMA 2018-008 = zubkovaite

Messaggio da Marco E. Ciriotti » mar 04 giu, 2019 12:26

Prossima pubblicazione.

▪ Pekov, I.V., Lykova, I.S., Agakhanov, A.A., Belakovskiy, D.I., Vigasina, M.F., Britvin, S.N., Turchkova, A.G., Sidorov, E.G., Scheidl, K.S. (2019): New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. XII. Zubkovaite, Ca3Cu3(AsO4)4. Mineralogical Magazine, 83, (in press).

The new mineral zubkovaite Ca3Cu3(AsO4)4 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 anhydrite, svabite, hematite, johillerite, tilasite, fluorophlogopite, potassic feldspar, and aphthitalite. Zubkovaite occurs as coarse prismatic crystals up to 0.01 x 0.01 x 0.2 mm3 combined in radiating aggregates or crusts. The mineral is transparent, bright sky-blue, turquoise-coloured or light bluish-green, with vitreous lustre. It is brittle, with imperfect cleavage. The Mohs’ hardness is ca 3. Dcalc is 4.161 g cm-3. Zubkovaite is optically biaxial (–), α 1.747(5), β 1.774(5), γ 1.792(5), 2Vmeas = 75(10)º. Chemical composition (wt.%, electron microprobe) is: CaO 19.22, CuO 27.37, As2O5 52.54, SO3 0.67, total 99.80. The empirical formula based on 16 O apfu is Ca2.96Cu2.97(As3.945S0.07)Σ4.015O16. Zubkovaite is monoclinic, C2, a 16.836(3), b 5.0405(8), c 9.1173(17) Å, β 117.388(13)º, V 687.0(2) Å3 and Z 2. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 7.44(100)(-201), 3.727(79)(400, -402, -311), 3.334(92)(-112), 2.914(73)(311), 2.765(50)(-601, -602), 2.591(96)(-313), and 2.521(53)(020). The crystal structure is unique for minerals. It was solved from single-crystal XRD data, R = 7.19%. The structure contains trimers of Cu2+-centred polyhedra (consisting of one distorted square CuO4 in the core and two distorted square pyramids CuO5) and two crystallographically independent As5+O4 tetrahedra playing different roles: As(2)O4 tetrahedra link neighbouring trimers into ribbons whereas As(1)O4 tetrahedra link adjacent ribbons into heteropolyhedral layers; Ca cations are located in the interlayer space. The mineral is named in honour of the Russian crystallographer and crystal chemist Natalia Vital’evna Zubkova (born 1976).
Marco E. Ciriotti

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