IMA 2016-010 = edtollite; IMA 2017-020 = alumoedtollite

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Marco E. Ciriotti
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IMA 2016-010 = edtollite; IMA 2017-020 = alumoedtollite

Messaggio da Marco E. Ciriotti » mer 03 ott, 2018 11:13

Prossima pubblicazione.

▪ Pekov, I.V., Zubkova, N.V., Agakhanov, A.A., Ksenofontov, D.A., Pautov, L.A., Sidorov, E.G., Britvin, S.N., Vigasina, M.F., Pushcharovsky, D.Y. (2018): New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. X. Edtollite, K2NaCu5Fe3+O2(AsO4)4, and alumoedtollite, K2NaCu5AlO2(AsO4)4. Mineralogical Magazine, 82, (in press).

Two new isostructural minerals edtollite K2NaCu5Fe3+O2(AsO4)4 and alumoedtollite K2NaCu5AlO2(AsO4)4 are found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. They are associated with sylvite, tenorite, dmisokolovite, shchurovskyite, johillerite, bradaczekite, orthoclase, etc. Edtollite forms prismatic crystals up to 0.02 x 0.1 mm; alumoedtollite forms long-prismatic crystals up to 0.01 x 0.1 mm. Both minerals have semi-metallic lustre. Edtollite is brown-black to black, alumoedtollite is bronze-coloured. Dcalc 4.26 (edtollite) and 4.28 (alumoedtollite) g·cm-3. In reflected light, both minerals are grey, with distinct anisotropy. Reflectance values [edtollite/alumoedtollite: R1–R2, %(λ, nm)] are: 8.3– 8.2/8.7–7.7(470), 7.7–7.4/8.3–7.4(546), 7.1–6.9/8.3–7.4(589), 6.3–6.3/7.6–7.2(650). Chemical data (wt.%, electron-microprobe; edtollite/alumoedtollite): Na2O 3.13/2.58, K2O 8.12/9.09, Rb2O 0.00/0.11, CaO 0.00/0.52, CuO 36.55/38.35, ZnO 0.46/0.00, Al2O3 0.00/3.48, Fe2O3 7.34/1.79, TiO2 0.27/0.00, As2O5 43.57/43.66, total 99.44/99.58. The empirical formulae, based on 18 O apfu, are: edtollite: K1.83Na1.07Cu4.88Zn0.06Fe3+0.98Ti0.04As4.03O18; alumoedtollite: K2.02Rb0.01Na0.87Ca0.10Cu5.06Al0.72Fe3+0.24As3.99O18. Both minerals are triclinic, P-1; unit-cell parameters (edtollite/alumoedtollite) are: a 5.1168(6)/5.0904(11), b 9.1241(12)/9.0778(14), c 9.6979(14)/9.6658(2) Å, alpha 110.117(13)/110.334(17), β 102.454(12)/102.461(19), gamma 92.852(11)/92.788(15)º, V 411.32(9)/404.88(14) Å3 and Z 1/1. The strongest reflections of PXRD patterns [d,Å(I)(hkl)] are: edtollite: 8.79(92)(001), 7.63(41)(0-11), 5.22(44)(011), 3.427(100)(012), 3.148(64)(0-13), 2.851(65)(-103) and 2.551(40)(-201); alumoedtollite: 8.78(81)(001), 7.62(67)(0-11), 3.418(100)(012), 3.147(52)(0-13), 2.558(58)(-122), 2.544(65)(-201) and 2.528(52)(-1-32). The crystal structures [single-crystal XRD, R = 0.0773 (edtollite) and 0.0826 (alumoedtollite); 1504 and 1046 unique reflections, respectively] represent a novel structure type. It is based upon heteropolyhedral pseudo-framework with the column formed by Cu2+-centred octahedra and square pyramids, octahedra MO6 (M = Fe3+, Al3+, Cu2+) and AsO4 tetrahedra as the main building unit. K+ and Na+ are located in wide and narrow channels, respectively. Edtollite is named after the Russian geologist and Arctic explorer Eduard Vasilievich Toll (1858–1902), alumoedtollite is its analogue with Al prevailing among trivalent cations.
Marco E. Ciriotti

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