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Crystal Chemistry of Chlormagaluminite, Mg4Al2(OH)12Cl2(H2O)2, a Natural Layered Double Hydroxide

1
Department of Crystallography, Institute of Earth Sciences, St. Petersburg State University, University Emb. 7/9, 199034 St. Petersburg, Russia
2
Institute of Volcanology and Seismology, Russian Academy of Sciences, Bulvar Piipa 9, 683006 Petropavlovsk-Kamchatsky, Russia
3
Nanomaterials Research Centre, Kola Science Centre, Russian Academy of Sciences, Fersman Street 14, 184209 Apatity, Russia
4
Department of Mineralogy, Faculty of Geology, Moscow State University, Leninskie Gory 1, 119991 Moscow, Russia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(4), 221; https://doi.org/10.3390/min9040221
Received: 16 March 2019 / Revised: 6 April 2019 / Accepted: 6 April 2019 / Published: 8 April 2019
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Abstract

Chlormagaluminite is the only Cl-dominated hydrotalcite-supergroup mineral species with M2+:M3+ = 2:1. The holotype sample of chlormagaluminite from the Kapaevskaya volcanic pipe (Irkutsk Oblast, Siberia, Russia) has been chemically and structurally characterized. The average chemical composition of the mineral is (electron microprobe, OH content is calculated by stoichiometry and H2O from the crystal-structure data, wt. %): MgO 33.85, FeO 1.09, Al2O3 22.07, Cl 14.72, H2Otot 30.96, Cl=O −3.39, total 99.30. The empirical formula based on Mg + Al + Fe = 6 atoms per formula unit (apfu) is [Mg3.91Fe2+0.07Al2.02(OH)12]Cl2.02(H2O)2.0(2). The crystal structure has been solved from single-crystal X-ray diffraction data in the space group P63/mcm, a = 5.268(3), c = 15.297(8) Å and V = 367.6(4) Å3. The refinement converged to R1 = 0.083 on the basis of 152 unique reflections with I > 2σ(I) collected at room conditions. The powder pattern contains standard reflections of a 2H polytype and two additional reflections [(010), d010 = 4.574 Å; (110), d110 = 2.647 Å] indicative of Mg and Al ordering according to the 3 × 3 superstructure. The structure is based upon brucite-type octahedral layers with an ordered distribution of Mg and Al over octahedral sites. The Cl anions and H2O molecules reside in the interlayer, providing a three-dimensional integrity of the structure. View Full-Text
Keywords: chlormagaluminite; layered double hydroxide; LDH; quintinite group; hydrotalcite supergroup; structure chlormagaluminite; layered double hydroxide; LDH; quintinite group; hydrotalcite supergroup; structure
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Zhitova, E.S.; Krivovichev, S.V.; Pekov, I.V.; Yapaskurt, V.O. Crystal Chemistry of Chlormagaluminite, Mg4Al2(OH)12Cl2(H2O)2, a Natural Layered Double Hydroxide. Minerals 2019, 9, 221.

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