This paper is the first description of natural copper-rich oxide spinels. They were found in deposits of oxidizing-type fumaroles related to the Tolbachik volcano, Kamchatka, Russia. This mineralization is represented by nine species with the following maximum contents of CuO (wt.%, given in parentheses): a new mineral thermaerogenite, ideally CuAl₂O₄ (26.9), cuprospinel, ideally CuFe³⁺₂O₄ (28.6), gahnite (21.4), magnesioferrite (14.7), spinel (10.9), magnesiochromite (9.0), franklinite (7.9), chromite (5.9), and zincochromite (4.8). Cuprospinel, formerly known only as a phase of anthropogenic origin, turned out to be the Cu-richest natural spinel-type oxide [sample with the composition (Cu_0.831Zn_0.100Mg_0.043Ni_0.022)_Σ0.996(Fe³⁺_1.725Al_0.219Mn³⁺_0.048Ti_0.008)_Σ2.000O₄ from Tolbachik]. Aluminum and Fe³⁺-dominant spinels (thermaerogenite, gahnite, spinel, cuprospinel, franklinite, and magnesioferrite) were deposited directly from hot gas as volcanic sublimates. The most probable temperature interval of their crystallization is 600–800 °C. They are associated with each other and with tenorite, hematite, orthoclase, fluorophlogopite, langbeinite, calciolangbeinite, aphthitalite, anhydrite, fluoborite, sylvite, halite, pseudobrookite, urusovite, johillerite, ericlaxmanite, tilasite, etc. Cu-bearing spinels are among the latest minerals of this assemblage: they occur in cavities and overgrow even alkaline sulfates. Cu-enriched varieties of chrome-spinels (magnesiochromite, chromite, and zincochromite) were likely formed in the course of the metasomatic replacement of a magmatic chrome-spinel in micro-xenoliths of ultrabasic rock under the influence of volcanic gases. The new mineral thermaerogenite, ideally CuAl₂O₄, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption. It forms octahedral crystals up to 0.02 mm typically combined in open-work clusters up to 1 mm across. Thermaerogenite is semitransparent to transparent, with a strong vitreous lustre. Its colour is brown, yellow-brown, red-brown, brown-yellow or brown-red. The mineral is brittle, with the conchoidal fracture, cleavage is none observed. D(calc.) is 4.87 g/cm³. The chemical composition of the holotype (wt.%, electron microprobe) is: CuO 25.01, ZnO 17.45, Al₂O₃ 39.43, Cr₂O₃ 0.27, Fe₂O₃ 17.96, total 100.12 wt.%. The empirical formula calculated on the basis of 4 O apfu is: (Cu_0.619Zn_0.422)_Σ1.041(Al_1.523Fe³⁺_0.443Cr_0.007)_Σ1.973O₄. The mineral is cubic, Fd-3m, a = 8.093(9) Å, V = 530.1(10) ų. Thermaerogenite forms a continuous isomorphous series with gahnite. The strongest lines of the powder X-ray diffraction pattern of thermaerogenite [d, Å (I, %) (hkl)] are: 2.873 (65) (220), 2.451 (100) (311), 2.033 (10) (400), 1.660 (16) (422), 1.565 (28) (511) and 1.438 (30) (440).

—The paper contains data on rutile, tripuhyite, and unusual Ti-rich cassiterite found in sublimates of active fumaroles at the Tolbachik volcano, Kamchatka, Russia. In contrast to rutile from other geological environments, fumarolic rutile is enriched in minor chalcophile elements. It contains up to (wt %): 35 Sb₂O₅, 59 SnO₂, 11.3 TeO₃, 1.9 CuO, 0.4 ZnO, and 18 Fe₂O₃. Such high Ti and Cu contents in rutile have not been published before, while minor Te contents have been measured for the first time. Cassiterite containing 19–23 wt % TiO₂ also is a new variety. Hexavalent tellurium is incorporated into the rutile structure together with trivalent iron according to the substitution scheme Te⁶⁺ + 2Fe³⁺ → 3Ti⁴⁺. In fumaroles of the Tolbachik volcano, isostructural rutile, tripuhyite, and cassiterite form a ternary system with several gaps. These minerals were formed at temperatures no lower than 350°C, most likely as a result of interaction between hot volcanic gas (a source for chalcophile elements) and basalt (a source for Ti).

Hematite from the fumaroles of the Tolbachik volcano (Kamchatka, Russia) was studied in detail. This fumarolic hematite contains significant admixtures of chalcophile elements: tin (up to 9.2 wt % SnO₂, the highest content known for natural hematite), copper (up to 4.7 wt % CuO), and for the first time antimony (up to 2.6 wt % Sb₂O₅). Other significant admixtures are represented by Ti, Mg, Mn, Al, and Cr. The previously unknown Sn–Cu- and Sn–Cu–Sb-bearing varieties of hematite were revealed, as well as new isomorphic schemes for this mineral: Sn⁴⁺ + Cu²⁺ → 2Fe³⁺ and Sb⁵⁺ + 2(Cu,Fe)²⁺ → 3Fe³⁺. It is shown that, in oxidizing-type Tolbachik fumaroles, hematite is the major concentrator of Fe, as well as Sn and Sb. The epitaxy of rutile-group minerals (cassiterite, rutile, and tripuhyite), oxide spinels (magnesioferrite, gahnite, and cuprospinel), and corundum is described. Hematite enriched in such admixtures was formed in the temperature range of 500–850°C. Volcanic gas was the source for chalcophile elements (Sn, Sb, Cu, Zn), whereas a source for hardly volatile components (Mg, Al, Cr, Ti) was basalt surrounding fumarole chambers; a mixed source is suggested for Fe, Mn, and V. The chalcophile specificity of admixed components is an indicative feature of fumarolic hematite. The finding of martite in Tolbachik fumaroles implies that the oxidizing potential increases in time during the fumarolic mineral formation.

This article provides data on cristobalite and tridymite from the Arsenatnaya active fumarole of the Tolbachik volcano, Kamchatka, Russia. The minerals occ

New data on the crystal structure and isomorphism of extra-framework components in the cancrinite-group mineral tounkite have been obtained using chemical and single-crystal X-ray diffraction data, as well as infrared, Raman, ESR, UV–Vis–near-IR absorption and photoluminescence spectroscopy methods. The crystal structure of tounkite is based on the aluminosilicate framework formed by the САСАСВСВСАСВ stacking sequence with ordered Si and Al atoms The framework hosts Losod and liottite cages as well as columns of cancrinite cages. It is shown that tounkite is characterized by wide variations of the chemical composition. Its simplified crystal–chemical formula is (Na⁺_3.89–5.18K⁺_0.15–1.64Ca²⁺_2.30–2.58(Al₆Si₆O₂₄)(SO₄²⁻,S₅²⁻,S₄) _2−x (Cl⁻, HS⁻)_1+y·nH₂O (x, y, n < 1). The S₂^⦁− and S₃^⦁− radical anions may occur in some tounkite samples in minor amounts. These crystal–chemical features indicate that tounkite crystallizes under highly reducing conditions. All studied tounkite samples were polysynthetic twins. A large 10-layed cage formed at the border between twin components, connected by a rotation of 180° around the [001] axis, which may host the large S₅²⁻ anion.

Hematite from Fumaroles of the Tolbachik Volcano (Kamchatka, Russia): Chemistry, Relationships with Associated Minerals, Morphological and Genetic Features Эксгаляционный гематит из фумарол вулкана Толбачик (Камчатка): типохимизм, морфогенетические особенности и взаимоотношения с другими минералами