Two novel compounds, K2Cu3(SO4)4 and KNaCu(SO4)2, were synthesized. The crystal structure of K2Cu3(SO4)4 is based on a [Cu3(SO4)4]2− framework with relatively simple bond topology, but with four different CuO n polyhedron geometries. The K+ cations reside in the pores of the framework. The [Cu(SO4)2]2− framework in KNaCu(SO4)2 encloses large elliptical channels running along [001]. Larger channels are occupied by K+, whereas smaller ones are filled by Na+. The bond-valence energy landscape (BVEL) approach has been demonstrated to be a useful method for the prediction of the mobility of alkali metal ions in various structures. By means of this approach, the threshold energies at which isosurfaces begin to percolate as well as the directions of possible ion migration in the structures were determined. The modelling of ion migration maps by the analysis of the procrystal electron-density distribution was used to rapidly identify ion migration pathways and limiting barriers between particular crystallographic sites in the structures under consideration. Its consistency and complementarity with the BVEL method have been demonstrated. Both approaches revealed a relatively low ion threshold percolation and migration barriers in the cryptochalcite-type structures [cryptochalcite: K2Cu5O(SO4)5]. Hence, one may assume that its 3D framework type is suited for ion transport applications. The review of all known members of the groups of anhydrous copper sulfates did not reveal a correlation between the porosity of the framework structures and a manifestation of ion conduction properties.

No abstract

A new mineral glikinite, ideally Zn3O(SO4)2, was found in high-temperature exhalative mineral assemblages in the Arsenatnaya fumarole, Second scoria cone of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Glikinite is associated closely with langbeinite, lammerite-β, bradaczekite, euchlorine, anhydrite, chalcocyanite and tenorite. It is monoclinic, P21/m, a = 7.298(18), b = 6.588(11), c = 7.840(12) Å, β = 117.15(3)°, V = 335.4(11) Å3 and R1 = 0.046. The eight strongest lines of the powder X-ray diffraction pattern [d in Å (I) (hkl)] are: 6.969(56)(00 $\bar{1}$ ), 3.942(52)(101), 3.483(100)(00 $\bar{2}$ ), 3.294(49)(020), 2.936(43)(120), 2.534(63)(201), 2.501(63)(20 $\bar{3}$ ) and 2.395(86)(02 $\bar{2}$ ). The chemical composition determined by electron-microprobe analysis is (wt.%): ZnO 42.47, CuO 19.50, SO3 39.96, total 101.93. The empirical formula calculated on the basis of O = 9 apfu is Zn2.07Cu0.97S1.98O9 and the simplified formula is Zn3O(SO4)2. Glikinite is a Zn,Cu analogue of synthetic Zn3O(SO4)2. The crystal structure of glikinite is based on OZn4 tetrahedra sharing common corners, thus forming [Zn3O]4+ chains. Sulfate groups interconnect [Zn3O]4+ chains into a 3D framework.

This is a 'preproof' accepted article for Mineralogical Magazine. This version may be subject to change during the production process.

Hydration processes of primary anhydrous minerals as well as dehydration of the hydrated phases are relevant not only for answering geochemical and petrological questions, but are also interesting in the context of the theory of the ‘Evolution of minerals’. Our study of the evolution of anhydrous exhalative sulfates in hydration and dehydration processes has demonstrated the complexity of the processes for a number of minerals from the active high-temperature fumaroles of Tolbachik volcano (chalcocyanite Cu(SO4), dolerophanite Cu2O(SO4), alumoklyuchevskite K3Cu3AlO2(SO4)4 and itelmenite Na2CuMg2(SO4)4). Hydration and dehydration experiments were carried out for all four minerals using powder X-ray diffraction. A typical structural characteristic of several anhydrous copper sulfate minerals of fumarolic origin is the presence of oxygen-centred OCu4 tetrahedra. These are absent in the structures of all known hydrated minerals or synthetic compounds of the class under consideration. Hydration of minerals initially containing O2– anions as part of oxocomplexes, proceeds with sequential formation of a large series of hydroxysalts. On the contrary, hydration of itelmenite with its relatively complex ‘initial’ structure, but without additional oxygen atoms that are strong Lewis bases, results in formation of simpler hydrates. The lower the temperature and the larger the excess of water, the stronger the tendency of the cations to adopt higher hydration numbers thus outcompeting the sulfate anions as ligands. Ultimately, the water molecules completely expel the bridging sulfate anions from the metal coordination sphere yielding relatively simple fully hydrated structures.

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 Na 2 CuMg 2 (SO 4 ) 4 , containing isomorphous admixture of Zn, was described in 2018, whereas glikinite, ideally Zn 3 O(SO 4 ) 2 , was described in 2020. Synthetic analogs of both minerals were obtained during studies of phase formation in the Na 2 SO 4 -CuSO 4 -MgSO 4 -(ZnSO 4 ) 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 Na 2 CuM 2 (SO 4 ) 4 stoichiometry. The Mg compound could be prepared single-phase which allowed the study of its thermal expansion and IR spectroscopy. Na 2 CuMg 2 (SO 4 ) 4 and Na 2 CuZn 2 (SO 4 ) 4 were evaluated for Na + -ion diffusion. For the Zn compound, several by-products were observed which are synthetic analogs of puninite Na 2 Cu 3 O(SO 4 ) 2 , as well as hermannjahnite CuZn(SO 4 ) 2 and glikinite-type (Zn,Cu) 3 O(SO 4 ) 2 . All of them were prepared via solid-state reactions in open systems. The Na 2 CuMg 2 (SO 4 ) 4 , Na 2 CuZn 2 (SO 4 ) 4 and (Zn,Cu) 3 O(SO 4 ) 2 were structurally characterized by the singlecrystal XRD. In the Zn-bearing system, the admixture of Cu 2+ likely controls the formation of itelmenitetype 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. The 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.

No abstract

Alkali copper sulfates form a rapidly developing family of inorganics. Herein, we report synthesis and crystal structure, and evaluate possible ion migration pathways for a novel Na-K-Cu anhydrous sulfate, K(Na,K)Na2[Cu2(SO4)4]. The CuO7 and SO4 polyhedra share common vertices and edges to form [Cu2(SO4)4]4− wide ribbons, which link to each other via common oxygen atoms forming the host part of the structure. Four guest alkali sites are occupied by solely K+, mixture of K+ and Na+, and solely Na+, which agrees well with the size of the cavities. The crystal structure of K(Na,K)Na2[Cu2(SO4)4] contains two symmetry-independent Cu sites with [4+1+(2)] coordination environments. The overall coordination polyhedra of Cu2+ can be considered as `octahedra with one split vertex'. A similar coordination mode was observed also in some other multinary copper sulfates, mostly of the mineral world. These coordination modes were reviewed and five types of CuO7 polyhedra are identified. CuO7 polyhedra are almost restricted to copper sulfates and phosphates. It was found that a larger amount of the smaller SO4 2− and PO4 3− anions can cluster around a single Cu2+ cation; in addition, for such relatively small anions, both mono (κ1) and bidentate (κ2) coordination modes to the Cu2+ are possible. The correlation between crystallographic characteristics and bond valence energies showed that the new copper sulfate framework, [Cu2(SO4)4]4−, contains one interconnected path suitable for Na+ mobility at tolerable activation energies and that K(Na,K)Na2[Cu2(SO4)4] can be considered as a potential candidate for novel Na-ion conductors.