New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. X. Edtollite, K2NaCu5Fe3+O2(AsO4)4, and alumoedtollite, K2NaCu5AlO2(AsO4)4. (August 2019)

• Record Type: Journal Article
• Authors: Pekov, Igor V.; Zubkova, Natalia V.; Agakhanov, Atali A.; Ksenofontov, Dmitry A.; Pautov, Leonid A.; Sidorov, Evgeny G.; Britvin, Sergey N.; Vigasina, Marina F.; Pushcharovsky, Dmitry Y.
• Is Part Of: Mineralogical magazine. Volume 83:Number 4(2019)
• Page Start: 485
• Page End: 495
• Publication Date: 2019-08
• Subjects: edtollite, -- alumoedtollite, -- new mineral, -- arsenate, -- crystal structure, -- fumarole sublimate, -- Tolbachik volcano, -- Kamchatka; Mineralogy -- Periodicals; Mineralogy -- Great Britain -- Periodicals; 549.05
• DOI: 10.1180/mgm.2018.155
• Languages: English
• ISSNs: 0026-461X

Abstract

Abstract: Two new isostructural minerals edtollite K2 NaCu5 Fe 3+ O2 (AsO4 )4 and alumoedtollite K2 NaCu5 AlO2 (AsO4 )4 have been 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, and orthoclase. Edtollite forms prismatic crystals up to 0.02 mm × 0.1 mm; alumoedtollite forms long-prismatic crystals up to 0.01 mm × 0.1 mm. Both minerals have a semi-metallic lustre. Edtollite is brown–black to black and alumoedtollite is bronze coloured. D calc. = 4.26 (edtollite) and 4.28 (alumoedtollite) g cm –3 . In reflected light, both minerals are grey, with distinct anisotropy. Reflectance values [edtollite/alumoedtollite: R 1 – R 2, % (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); and 6.3–6.3/7.6–7.2 (650). Chemical data are: (edtollite/alumoedtollite, wt.%, electron-microprobe): Na2 O 3.13/2.58, K2 O 8.12/9.09, Rb2 O 0.00/0.11, CaO 0.00/0.52, CuO 36.55/38.35, ZnO 0.46/0.00, Al2 O3 0.00/3.48, Fe2 O3 7.34/1.79, TiO2 0.27/0.00, As2 O5 43.57/43.66, total 99.44/99.58. The empirical formulae, based on 18 O apfu, for edtollite is: K1.83 Na1.07 Cu4.88 Zn0.06 Fe 3+ 0.98 Ti0.04 As4.03 O18 ; and for alumoedtollite is: K2.02 Rb0.01 Na0.87 Ca0.10 Cu5.06 Al0.72 Fe 3+ 0.24 As3.99 O18 . Both minerals are triclinic, P $\bar{1}$ ; 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, α = 110.117(13)/110.334(17), β = 102.454(12)/102.461(19), γ = 92.852(11)/92.788(15)°, V = 411.32(9)/404.88(14) Å 3 and Z = 1/1. The strongest reflections in the powder X-ray diffraction pattern [ d, Å( I )( hkl )] are for edtollite: 8.79(92)(001), 7.63(41)(0 $\bar{1}$ 1), 5.22(44)(011), 3.427(100)(012), 3.148(64)(0 $\bar{1}$ 3), 2.851(65)( $\bar{1}$ 03) and 2.551(40)( $\bar{2}$ 01); and for alumoedtollite: 8.78(81)(001), 7.62(67)(0 $\bar{1}$ 1), 3.418(100)(012), 3.147(52)(0 $\bar{1}$ 3), 2.558(58)( $\bar{1}$ 22), 2.544(65)( $\bar{2}$ 01) and 2.528(52)( $\bar{1}\bar{3}$ 2). The crystal structures [single-crystal X-ray diffraction, R = 0.0773 (edtollite) and 0.0826 (alumoedtollite); 1504 and 1046 unique reflections, respectively] represent a novel structure type. It is based upon a heteropolyhedral pseudo-framework with the column formed by Cu 2+ -centred octahedra and square pyramids, octahedra M O6 ( M = Fe 3+, Al 3+ or Cu 2+ ) 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.