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A New Mineral Ferrisanidine, K[Fe3+Si3O8], the First Natural Feldspar with Species-Defining Iron

1
Faculty of Geology, Moscow State University, Vorobievy Gory, Moscow 119991, Russia
2
Department of Crystallography, St Petersburg State University, University Embankment 7/9, St Petersburg 199034, Russia
3
Nanomaterials Research Center, Kola Science Center of Russian Academy of Sciences, Fersman Str. 14, Apatity 184209, Russia
4
Institute of Volcanology and Seismology, Far Eastern Branch of Russian Academy of Sciences, Piip Boulevard 9, Petropavlovsk-Kamchatsky 683006, Russia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(12), 770; https://doi.org/10.3390/min9120770
Received: 10 November 2019 / Revised: 6 December 2019 / Accepted: 9 December 2019 / Published: 11 December 2019
(This article belongs to the Collection New Minerals)
Ferrisanidine, K[Fe3+Si3O8], the first natural feldspar with species-defining iron, is an analogue of sanidine bearing Fe3+ instead of Al. It was found in exhalations of the active Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Fissure Tolbachik Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. The associated minerals are aegirine, cassiterite, hematite, sylvite, halite, johillerite, arsmirandite, axelite, aphthitalite. Ferrisanidine forms porous crusts composed by cavernous short prismatic crystals or irregular grains up to 10 μm × 20 μm. Ferrisanidine is transparent, colorless to white, the lustre is vitreous. Dcalc is 2.722 g·cm−3. The chemical composition of ferrisanidine (wt. %, electron microprobe) is: Na2O 0.25, K2O 15.15, Al2O3 0.27, Fe2O3 24.92, SiO2 60.50, in total 101.09. The empirical formula calculated based on 8 O apfu is (K0.97Na0.03)Ʃ1.00(Si3.03Fe3+0.94Al0.02)Ʃ3.99O8. The crystal structure of ferrisanidine was studied using the Rietveld method, the final R indices are: Rp = 0.0053, Rwp = 0.0075, R1 = 0.0536. Parameters of the monoclinic unit cell are: a = 8.678(4), b = 13.144(8), c = 7.337(5) Å, β = 116.39(8)°, V = 749.6(9) Å3. Space group is C2/m. The crystal structure of ferrisanidine is based on the sanidine-type “ferrisilicate” framework formed by disordered [SiO4] and [Fe3+O4] tetrahedra. View Full-Text
Keywords: ferrisanidine; new mineral; sanidine; feldspar group; iron in feldspar; crystal structure; fumarole; Tolbachik volcano; Kamchatka ferrisanidine; new mineral; sanidine; feldspar group; iron in feldspar; crystal structure; fumarole; Tolbachik volcano; Kamchatka
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Shchipalkina, N.V.; Pekov, I.V.; Britvin, S.N.; Koshlyakova, N.N.; Vigasina, M.F.; Sidorov, E.G. A New Mineral Ferrisanidine, K[Fe3+Si3O8], the First Natural Feldspar with Species-Defining Iron. Minerals 2019, 9, 770.

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