Abstract
Anhydrous sulfate minerals are abundant in the active fumaroles with highly oxidizing conditions on the scoria cones of the Tolbachik volcano. The mineral itelmenite, ideally Na2CuMg2(SO4)4, containing isomorphous admixture of Zn, was described in 2018, whereas glikinite, ideally Zn3O(SO4)2, was described in 2020. Synthetic analogs of both minerals were obtained during studies of phase formation in the Na2SO4–CuSO4–MgSO4–(ZnSO4) systems which lead to essentially different results. Solid-state syntheses resulted in formation of several compounds previously known as minerals only. Both Zn- and Mg-containing analogs of itelmenite were prepared and exhibit slight deviations from the ideal Na2CuM2(SO4)4 stoichiometry. The Mg compound could be prepared single-phase which allowed the study of its thermal expansion and IR spectroscopy. Na2CuMg2(SO4)4 and Na2CuZn2(SO4)4 were evaluated for Na+-ion diffusion. For the Zn compound, several by-products were observed which are synthetic analogs of puninite Na2Cu3O(SO4)2, as well as hermannjahnite CuZn(SO4)2 and glikinite-type (Zn,Cu)3O(SO4)2. All of them were prepared via solid-state reactions in open systems. The Na2CuMg2(SO4)4, Na2CuZn2(SO4)4 and (Zn,Cu)3O(SO4)2 were structurally characterized by the single-crystal XRD. In the Zn-bearing system, the admixture of Cu2+ likely controls the formation of itelmenite-type and glikinite-type phases. The results of the experiments allowed to deduce possible scenarios of the formation processes of itelmenite and some other endemic fumarolic minerals. Our study shows that outstanding mineralogical diversity observed in the fumaroles of the Tolbachik scoria cones is not only due to the formation from the gas enriched by transition metals and involves also intensive exchange with the host basaltic scoria. Similar processes seem also to be responsible for the recrystallization of many other mineral species observed in high-temperature fumaroles resulted from the recent eruptions.
Highlights
Minerals containing sulfate anions constitute one of the most diverse groups in terrestrial environments
Our experiments indicate that investigation of anhydrous sulfate systems reproduces many compounds known before as mineral species only
It appeared possible to obtain the Zn- and Mg-analogs of itelmenite. The latter was obtained as a pure phase which allowed the study of thermal expansion
Summary
Physics and Chemistry of Minerals (2021) 48:6 anhydrous sulfates with alkali (and transition) metals is their high solubility. Essential endothermal effects are observed in the 477–526 °C range (corresponding maxima at 485 and 505 °C) accompanied by the mass loss of 0.05%. Crystallization of a multiphase sample (Fig. 1c), containing the desired Na2CuZn2(SO4), proceeds at essentially lower temperatures compared to its magnesium-based analog. This process is reflected by two very strong thermal effects. An endothermal event starts at 583 °C, reaching its maximum at 678 °C and completing at 691 °C; the mass loss is 1.40% This is rather common for decomposition processes, yet no peaks were observed on the IC curves.
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