A fumarole in a one-pot: synthesis, crystal structure and properties of Zn- and Mg-analogs of itelmenite and a synthetic analog of glikinite

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)(3)O(SO4)(2). All of them were prepared via solid-state reactions in open systems. The Na2CuMg2(SO4)(4), Na2CuZn2(SO4)(4) and (Zn,Cu)(3)O(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.

Automated summary

The abundant anhydrous sulfate minerals in the active fumaroles of the Tolbachik volcano scoria cones were studied, resulting in the synthesis of synthetic analogs of itelmenite and glikinite minerals, showing slight deviations from their ideal stoichiometry. Analysis of Na+-ion diffusion allowed for possible scenarios of mineral formation processes to be deduced.