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A new mineral nishanbaevite, ideally KAl2O(AsO4)(SO4), was found in sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with euchlorine, alumoklyuchevskite, langbeinite, urusovite, lammerite, lammerite-β, ericlaxmanite, kozyrevskite, and hematite. Nishanbaevite occurs as long-prismatic or lamellar crystals up to 0.03 mm typically combined in brush-like aggregates and crusts up to 1.5 mm across. It is transparent, colourless, with vitreous lustre. Dcalc = 3.011 g cm− 3. Nishanbaevite is optically biaxial (–), α = 1.552, β ≈ γ = 1.567. The chemical composition (average of seven analyses) is: Na2O 3.79, K2O 8.01, CaO 0.10, CuO 0.21, Al2O3 30.08, Fe2O3 0.50, SiO2 1.62, P2O5 0.66, As2O5 32.23, SO3 22.59, total 99.79 wt.%. The empirical formula calculated based on 9 O apfu is: (K0.57Na0.41Ca0.01)Σ0.99(Al1.99Fe3+0.02Cu0.01)Σ2.02(As0.95S0.95Si0.09P0.03)Σ2.02O9. Nishanbaevite is orthorhombic, Pbcm, a = 15.487(3), b = 7.2582(16), c = 6.6014(17) Å, V = 742.1(3) Å3 and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 15.49(100)(100), 6.56(30)(110), 4.653(29)(111), 3.881(54)(400), 3.298(52)(002), 3.113(29)(121), and 3.038(51)(202, 411). The crystal structure, solved from single-crystal XRD data (R = 7.58%), is unique. It is based on the complex heteropolyhedral sheets formed by zig-zag chains of Al-centred polyhedra (alternating trigonal bipyramids AlO5 and octahedra AlO6 sharing edges) and isolated tetrahedra AsO4 and SO4. Adjacent chains of Al polyhedra are connected via AsO4 tetrahedra to form a heteropolyhedral double-layer. Its topological peculiarity is considered and compared with those in structurally related compounds. The (K,Na) site is located in the interlayer space between SO4 tetrahedra. The position of nishanbaevite among the arsenate-sulfates and their specific structural features are discussed. The mineral is named in honour of the Russian mineralogist Tursun Prnazorovich Nishanbaev (1955–2017).

The new mineral yurgensonite, ideally K2SnTiO2(AsO4)2, the first natural arsenate with species-defining tin, and the continuous isomorphous series between yurgensonite and katiarsite KTiO(AsO4) are described from sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Yurgensonite and a Sn-bearing variety of katiarsite are associated closely with one another and with badalovite, pansnerite, yurmarinite, achyrophanite, arsenatrotitanite, hatertite, khrenovite, svabite, sanidine, hematite, cassiterite, rutile and aphthitalite-group sulfates. Yurgensonite occurs as sword-shaped crystals up to 0.01 mm × 0.05 mm × 1 mm or acicular to hair-like individuals up to 1 mm long, typically forming radial aggregates up to 2 mm across. It is transparent, colourless, white or pale beige, with vitreous lustre. The mineral is brittle, cleavage was not observed. Dcalc is 3.877 g cm-3. Yurgensonite is optically biaxial (–), α = 1.764(6), β = 1.780(6), γ = 1.792(6) and 2Vmeas. is large. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 0.51, K2O 16.27, Rb2O 0.12, Al2O3 0.26, Fe2O3 4.33, SiO2 0.29, TiO2 10.17, SnO2 22.01, P2O5 0.14, V2O5 0.19, As2O5 40.20, Sb2O5 4.88, SO3 0.28, total 99.65. The empirical formula based on 10 O apfu is (K1.92Na0.09Rb0.01)Σ2.02(Sn0.81Ti0.71Fe3+0.30Sb5+0.17Al0.03)Σ2.02(As1.945Si0.03S0.02P0.01V0.01)Σ2.015O10. Yurgensonite is orthorhombic, Pna21, a = 13.2681(6), b = 6.6209(3), c = 10.8113(5) Å, V = 949.74(7) Å3 and Z = 4. The crystal structure was solved from single-crystal X-ray diffraction data, R = 5.02%. Yurgensonite belongs to the KTP-structure type. It is a Ti,Sn-ordered analogue of katiarsite. The structure contains chains of corner-linked alternating crystallographically non-equivalent octahedra M(1) and M(2). In yurgensonite, Sn4+ prevails in the M(2)O6 octahedron whereas the M(1) site is Ti4+-dominant. The new mineral is named in honour of the Russian mineralogist, geochemist and specialist in studies of ore deposits Professor Georgiy Aleksandrovich Yurgenson (born 1935).

The new mineral vasilseverginite, ideally Cu9O4(AsO4)2(SO4)2, was found in the Arsenatnaya fumarole at the second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with tenorite, lammerite, stranskiite, lammerite-β, langbeinite, dolerophanite, sanidine, hematite, and gahnite. Vasilseverginite occurs as prismatic crystals up to 0.02 × 0.02 × 0.06 mm3 combined in groups or interrupted crusts up to 1 × 2 cm2 in area and up to 0.1 mm thick. It is transparent, bright green, with vitreous luster. Dcalc is 4.41 g·cm−3. Vasilseverginite is optically biaxial (–), α 1.816(5), β 1.870(5), γ 1.897(5), estimated 2V is 30(15)°. Chemical composition (wt%, electron-microprobe) is: CuO 64.03, ZnO 0.79, Fe2O3 0.25, P2O5 0.05, As2O5 20.83, SO3 14.92, total 100.87. The empirical formula calculated on O = 20 apfu is (Cu8.78Zn0.11Fe0.033+)Σ8.92As1.98P0.01S2.03O20. Vasilseverginite is monoclinic, P21/n, a = 8.1131(4), b = 9.9182(4), c = 11.0225(5) Å, β = 110.855(2)°, V = 828.84(6) Å3, and Z = 2. The strongest reflections in the powder XRD pattern [d,Å(I)(hkl)] are: 7.13(41)(101), 5.99(70)(110, 111), 5.260(100)(101), 4.642(46)(111), 3.140(31)(031), 2.821(35)(023), 2.784(38)(132, 032), 2.597(35)(204), and 2.556(50) (231, 212). The crystal structure, solved using single-crystal X-ray diffraction data, R1 = 0.025, is based upon complex [O4Cu9]10+ layers parallel to (101) that are composed of edge- and corner-sharing (OCu4) tetrahedra. The topology is unprecedented in inorganic structural chemistry. The crystal structure can be considered a hybrid of the structures of popovite Cu5O2(AsO4)2 and dolerophanite Cu2O(SO4) according to the scheme Cu9O4(AsO4)2(SO4)2 = Cu5O2(AsO4)2 + 2Cu2O(SO4). The chemical hybridization does not result in a significant increase in chemical complexity of vasilseverginite compared to the sum of those of popovite and dolerophanite, whereas the structural hybridization leads to the doubling of structural information per unit cell. The mineral is named in memory of the outstanding Russian mineralogist, geologist, and chemist Vasiliy Mikhailovich Severgin (1765–1826).

—In the $${\text{Cu}}_{3}^{{2 + }}$$ (T5+O4)2 (T = As, V or P) natural system arsenates are trimorphous (lammerite, lammerite-β, and unnamed triclinic Cu3[(As,V)O4]2), as well as vanadates (mcbirneyite, pseudolyonsite, and borisenkoite), while phosphates are represented by a poorly studied lammerite-like Cu3[(P,As)O4]2 phase. In active oxidizing-type fumaroles related to the Tolbachik volcano in Kamchatka, Russia, all these minerals crystallized at temperature no lower than 250°C. The crystal structure of natural triclinic Cu3[(As,V)O4]2 was first studied on a single crystal from the Yadovitaya fumarole at Tolbachik; R = 4.89%. It is isostructural to stranskiite and mcbirneyite and crystallizes in the P-1 space group; the unit-cell parameters are: a = 5.0701(8), b = 5.4047(8), c = 6.3910(8) A, α = 70.091(13), β = 86.828(12), γ = 68.399(15)°, V = 152.61(4) A3, and Z = 1. This paper also contains new data on mcbirneyite (its novel As-enriched variety is characterized), lammerite, and lammerite-β. Original and previously published materials on natural members of the Cu3(T5+O4)2 system are summarized and isomorphism and other crystal chemical features of minerals belonging to this system are discussed in comparison with the data on related synthetic compounds.

An unusual highly hydrated and Na-depleted variety of elpidite was identified in a hydrothermally altered peralkaline pegmatite at Mt. Yukspor in the Khibiny alkaline complex, Kola Peninsula, Russia. It differs from ‘ordinary’ elpidite, ideally Na2ZrSi6O15⋅3H2O, in its crystal chemical features, infrared spectrum and optical characteristics. The chemical composition (wt.%, electron microprobe, H2O by TGA) is: Na2O 5.45, K2O 0.67, CaO 0.05, SiO2 60.32, TiO2 1.34, ZrO2 18.43, Nb2O5 0.65, H2O 12.80, total 99.71. The empirical formula calculated on the basis of 6 Si and 15 O atoms is [(Na1.05K0.08Ca0.01)Σ1.14(H3O)0.74]Σ1.88(Zr0.89Ti0.10Nb0.03)Σ1.02Si6O15⋅3.47H2O; the H2O:H3O ratio was calculated from the charge balance requirement, taking into account the results of crystal structure refinement. The highly hydrated variety of elpidite is orthorhombic, Pma2, a = 14.5916(6), b = 7.3294(3), c = 7.1387(2) Å, V = 763.47(5) Å3 and Z = 2. The crystal structure was solved from single-crystal X-ray diffraction data, R1 = 3.43%. The structure is based upon an elpidite-type heteropolyhedral Zr–Si–O framework with Na+ and H3O+ cations and H2O molecules in the zeolitic channels. Hydronium cations substitute for water molecules in one of the extra-framework sites. This variety of elpidite could be considered as an intermediate product of natural ion-exchange reaction between ‘ordinary’ elpidite and a low-temperature hydrothermal fluid.

The new mineral eleomelanite, (K2Pb)Cu4O2(SO4)4, was found in the Arsenatnaya fumarole on the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik Volcano, Kamchatka, Russia. It is associated with euchlorine, fedotovite, wulffite, chalcocyanite, dolerophanite, dravertite, hermannjahnite, alumoklyuchevskite, klyuchevskite, piypite, cryptochalcite, cesiodymite, anglesite, langbeinite, calciolangbeinite, metathénardite, belomarinaite, aphthitalite, krasheninnikovite, steklite, anhydrite, hematite, tenorite, sanidine, sylvite, halite, lammerite, urusovite, and gold. Eleomelanite occurs as interrupted crusts up to 6 mm across and up to 0.3 mm thick consisting of equant, prismatic, or tabular crystals or grains up to 0.3 mm. It is translucent and black. The luster is oleaginous on crystal faces and vitreous on a cleavage surface. Dcalc is 3.790 g/cm3. Eleomelanite is optically biaxial (–), α 1.646(3), β 1.715(6), γ 1.734(6), 2Vmeas. = 60(15)°. The chemical composition (wt.%, electron-microprobe) is K2O 9.62, Rb2O 0.49, Cs2O 0.24, CaO 1.23, CuO 35.28, PbO 19.25, SO3 34.78, total 100.89. The empirical formula calculated based on 18 O apfu is (K1.88Pb0.79Ca0.20Rb0.05Cs0.02)Σ2.94Cu4.07S3.99O18. Eleomelanite is monoclinic, P21/n, a 9.3986(3), b 4.8911(1), c 18.2293(5) Å, β 104.409(3)°, V 811.63(4) Å3, and Z = 2. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 7.38(44)(101), 3.699(78)(112), , 3.173(40)(211), 2.915(35)(114), 2.838(35)(204), , and . The crystal structure was solved using single-crystal XRD data, R1 = 4.78%. It is based on heteropolyhedral Cu–S–O chains composed of Cu-centered polyhedra with [4+1+1] Cu2+ coordination and SO4 tetrahedra. Adjacent Cu–S–O chains are connected via chains of (K,Pb)O8 and KO10 polyhedra. Eleomelanite belongs to a novel structure type but has common structural features with klyuchevskite, alumoklyuchevskite, wulffite, parawulffite, and piypite. The name is derived from the Greek ελαιν (eleon), oil, and μλας (melas), black, due to its black color and oleaginous luster on crystal faces that are uncommon for sulfate minerals.

The new alluaudite-group mineral badalovite was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with hematite, tenorite, cassiterite, johillerite, nickenichite, calciojohillerite, bradaczekite, metathénardite, aphthitalite, langbeinite, calciolangbeinite, sanidine, fluorophlogopite, fluoborite, tilasite, anhydrite, pseudobrookite, sylvite, halite, lammerite, urusovite, ericlaxmanite, arsmirandite, svabite, krasheninnikovite, euchlorine, wulffite and alumoklyuchevskite. Badalovite forms oblique-angled prismatic crystals up to 1 mm × 1 mm × 5 mm, typically combined in groups or crusts up to several hundred cm2 in area. The mineral is transparent, green, grey, yellow or colourless, with vitreous lustre. It is brittle, the Mohs hardness is 3½. Cleavage was not observed, the fracture is uneven. Dcalc is 4.02 g cm–3. Badalovite is optically biaxial (–), α = 1.753(3), β = 1.757(3), γ = 1.758(3) and 2Vmeas. = 50(10)°. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 9.23, K2O 0.19, CaO 2.04, MgO 13.78, MnO 0.31, CuO 0.12, ZnO 0.24, Al2O3 0.06, Fe2O3 12.77, TiO2 0.01, SiO2 0.06, P2O5 0.33, V2O5 0.05, As2O5 61.51, SO3 0.02, total 100.72. The empirical formula based on 12 O apfu is Na1.67Ca0.20K0.02Mg1.92Zn0.02Mn0.02Cu0.01Fe3+0.90Al0.01(As3.01P0.03Si0.01)Σ3.05O12. The simplified formula is Na2Mg2Fe3+(AsO4)3. Badalovite is monoclinic, C2/c, a = 11.9034(3), b = 12.7832(2), c = 6.66340(16) Å, β = 112.523(3)°, V = 936.59(4) Å3 and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 6.41(38)(020), 5.505(20)(200), 3.577(23)($\bar{1}$31), 3.523(25)(310), 3.211(46)($\bar{1}$12), 2.911(28)($\bar{2}$22, $\bar{3}$12), 2.765(100)(240, 400) and 2.618(26)($\bar{1}$32). The crystal structure was solved from single-crystal XRD data with an R1 of = 2.49%. Badalovite is isostructural with other alluaudite-group minerals. Its simplified crystal chemical formula is A(1)NaA(1)’□A(2) □A(2)’NaM(1)MgM(2)(Mg0.5Fe3+0.5)2(AsO4)3 (□ – vacancy) and the end-member formula is NaNaMg(MgFe3+)(AsO4)3. The mineral is named in honour of the outstanding mineralogist and geochemist Stepan Tigranovich Badalov (1919–2014).

—We overview recent data on the mineralogy of oxidizing-type fumaroles of the Tolbachik Volcano (Kamchatka, Russia), with the main focus on the chemical specifics of the minerals. The active fumarole fields of Tolbachik are the most prominent mineral-forming exhalative system of this type in the world. About 350 mineral species, including 123 minerals first discovered here, are reliably identified in the Tolbachik fumaroles. The species diversity and the specifics of this mineralization are due to the unique combination of the physicochemical conditions and mechanisms of its formation: high temperatures, atmospheric pressure, superhigh oxygen fugacity, gas transport of most of chemical elements, and direct deposition of many high-temperature minerals from volcanic gases with a specific geochemical composition, including strong enrichment in alkaline metals and chalcophile (“ore”) elements. Sublimate silicates and minerals of As, Cu, Zn, Mn, Ti, Sn, Sb, Se, Au, Ag, Cs, Tl, and F are briefly described in terms of mineral geochemistry.

The new mineral kainotropite Cu4Fe3+O2(V2O7)(VO4) was found in sublimates of fumaroles related to the Tolbachik volcano, Kamchatka, Russia. The holotype specimen originates from the Yadovitaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption; associated minerals are hematite, langbeinite, calciolangbeinite, tenorite, piypite, lyonsite, rutile, pseudobrookite, sanidine, and lammerite. In paleo-fumarolic deposits of Mountain 1004 kainotropite is associated with diopside and hematite. It forms prismatic crystals up to 0.2 × 0.2 × 0.5 mm3, isolated or combined in clusters up to 0.7 mm across. Kainotropite is iron-black to reddish-black, with semi-metallic luster. Dcalc is 4.10 g/cm3. In reflected light, kainotropite is grey, weakly anisotropic. The reflectance values [Rmax–Rmin,% (λ, nm)] are: 18.3–17.3 (470), 17.3–16.3 (546), 16.9–15.7 (589), 16.3–15.1 (650). The chemical composition of the holotype sample (wt.%, electron microprobe) is: CuO 46.69, Al2O3 1.40, Fe2O3 10.04, TiO2 0.32, V2O5 37.58, As2O5 2.55, MoO3 0.76, total 99.34. The empirical formula, based on 13 O apfu, is: Cu3.96Fe3+0.85Al0.19Ti0.03(V2.78As0.15Mo0.04)Σ2.97O13. Kainotropite is orthorhombic, Pnma, a = 14.139(2), b = 6.7102(7), c = 11.4177(15) Å, V = 1083.3(2) Å3, and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 8.89(100)(101), 5.728(33)(002), 3.698(35)(212), 3.357(52)(020,203), 3.034(77)(220), 2.968(60)(303), and 2.655(27)(321,204). The crystal structure was solved from single-crystal XRD data, R = 0.085. Kainotropite represents a novel structure type. Cu2+ polyhedra (distorted tetragonal pyramids and strongly distorted octahedra) and Fe3+ octahedra are connected via common edges to form zigzag ribbons. Adjacent ribbons are connected by both V2O7 and VO4 groups (isolated from each other) to form a heteropolyhedral pseudo-framework. The name kainotropite is derived from the Greek word καινóτρoπoς, unusual, in allusion to its uncommon (for natural vanadates) anionic composition: it is the first mineral containing both pyrovanadate (V2O7)4– and orthovanadate (VO4)3– anions.

The new mineral pansnerite, ideally K3Na3Fe3+6(AsO4)8, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with aphthitalite, hematite, sanidine, badalovite, khrenovite, achyrophanite, arsenatrotitanite, ozerovaite, tilasite, calciojohillerite, johillerite, nickenichite, svabite, katiarsite, yurmarinite, anhydrite, rutile, cassiterite and pseudobrookite. Pansnerite forms tabular to lamellar (flattened on {010}), usually pseudo-hexagonal crystals up to 0.2 mm × 0.7 mm × 1 mm and crystal clusters up to 2 mm across. It is transparent to translucent, light green, pale greenish, yellowish–greenish or yellowish, with vitreous lustre. The mineral is brittle, with perfect {010} cleavage. The Mohs’ hardness is ca 3. Dcalc is 3.596 g cm–3. Pansnerite is optically biaxial (–), α = 1.702(4), β = 1.713(4), γ = 1.717(4), 2Vmeas = 45(10)° and 2Vcalc = 62°. Chemical composition (holotype, wt.%, electron microprobe data) is: Na2O 6.39, K2O 8.52, CaO 0.08, MgO 0.08, MnO 0.02, NiO 0.02, CuO 1.35, ZnO 0.34, Al2O3 7.35, Cr2O3 0.04, Fe2O3 16.72, SiO2 0.16, P2O5 0.22, V2O5 0.09, As2O5 57.76, SO3 0.04, total 99.20. The empirical formula based on 32 O apfu is K2.86Na3.26Ca0.02(Fe3+3.31Al2.28Cu0.27Zn0.07Mg0.03Cr0.01)Σ5.97(As7.95P0.05Si0.04V0.02S0.01)Σ8.06O32. Pansnerite is orthorhombic, Cmce, a = 10.7372(3), b = 20.8367(8), c = 6.47335(15) Å, V = 1448.27(7) Å3 and Z = 2. The strongest reflections of the X-ray powder diffraction pattern [d,Å(I)(hkl)] are: 10.49(100)(020), 5.380(88)(111), 4.793(65)(220), 3.105(46)(311, 002), 3.079(32)(112, 061), 2.932(35)(260), 2.783(65)(202) and 2.694(52)(400, 222). The crystal structure was solved from single-crystal X-ray diffraction data, R1 = 2.82%. The structure is based on heteropolyhedral layers formed by MO6 octahedra (M = Fe3+ and Al) sharing common vertices and connected by AsO4 tetrahedra. Na+ and K+ cations are located in the interlayer space. The mineral is named in honour of the German–Russian mineralogist and geographer Lavrentiy Ivanovich Pansner (1777–1851). Pansnerite forms a solid-solution series with the isotypic mineral ozerovaite, ideally KNa2Al3(AsO4)4.

The new mineral zubkovaite, Ca3Cu3(AsO4)4, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with anhydrite, svabite, hematite, johillerite, tilasite, fluorophlogopite, sanidine and aphthitalite. Zubkovaite occurs as coarse prismatic crystals up to 0.01 mm × 0.01 mm × 0.2 mm combined in radiating aggregates or crusts. The mineral is transparent, bright sky-blue, turquoise-coloured or light bluish-green, with vitreous lustre. It is brittle, with imperfect cleavage. The Mohs’ hardness isca3.Dcalcis 4.161 g cm–3. Zubkovaite is optically biaxial (–), α = 1.747(5), β = 1.774(5), γ = 1.792(5) and 2Vmeas= 75(10)°. Chemical composition (wt.%, electron microprobe) is: CaO 19.22, CuO 27.37, As2O552.54, SO30.67, total 99.80. The empirical formula based on 16 O apfu is Ca2.96Cu2.97(As3.945S0.07)Σ4.015O16. Zubkovaite is monoclinic,C2,a= 16.836(3),b= 5.0405(8),c= 9.1173(17) Å, β = 117.388(13)°,V= 687.0(2) Å3andZ= 2. The strongest reflections of the powder XRD pattern [d,Å (I) (hkl)] are: 7.44 (100) ($\bar 2$01), 3.727 (79) (400,$\bar 2$02,$\bar 3$11), 3.334 (92) ($\bar 1$12), 2.914 (73) (311), 2.765 (50) ($\bar 6$01,$\bar 6$02), 2.591 (96) ($\bar 3$13) and 2.521 (53) (020). The crystal structure is unique for minerals. It was solved from single-crystal X-ray diffraction data toR= 7.19%. The structure contains trimers of Cu2+-centred polyhedra (consisting of one distorted square CuO4in the core and two distorted square pyramids CuO5) and two crystallographically independent As5+O4tetrahedra playing different roles: As(2)O4tetrahedra link neighbouring trimers into ribbons whereas As(1)O4tetrahedra link adjacent ribbons into heteropolyhedral layers; Ca cations are located in the interlayer space. The mineral is named in honour of the Russian crystallographer and crystal chemist Natalia Vital'evna Zubkova (born 1976).

The new mineral antofagastaite, ideally Na2Ca(SO4)2·1.5H2O, was found in the oxidation zone of sulfide–quartz veins at the abandoned Coronel Manuel Rodríguez mine, Mejillones, Antofagasta Province, Antofagasta Region, Chile. It is associated with sideronatrite, metasideronatrite, aubertite, gypsum, ferrinatrite, glauberite, amarillite and an unidentified Fe phosphate. Antofagastaite occurs as prismatic crystals up to 0.5 mm × 1 mm × 5 mm, elongated along [010], typically combined in open-work aggregates up to 1 cm across. Antofagastaite is transparent and colourless, with vitreous lustre. It is brittle; the Mohs’ hardness isca3. Cleavage is distinct on (001).Dmeas.is 2.42(1) andDcalc.is 2.465 g cm−3. Antofagastaite is optically biaxial (–), α = 1.489(2), β = 1.508(2), γ = 1.510(2) and 2Vmeas.= 40(10)°. The IR spectrum is reported. Chemical composition (wt.%, electron microprobe, H2O determined by gas chromatography) is: Na2O 20.85, CaO 17.42, SO352.56, H2O 7.93, total 98.76. The empirical formula (based on 8 O atoms belonging to sulfate anions per formula unit with all H belonging to H2O molecules) is Na2.06Ca0.95S2.01O8·1.35H2O. Antofagastaite is monoclinic,P21/m,a= 6.4596(4),b= 6.8703(5),c= 9.4685(7) Å, β = 104.580(4)°,V= 406.67(5) Å3andZ= 2. The strongest reflections of the powder XRD pattern [d, Å (I, %) (hkl)] are: 9.17 (100) (001), 5.501 (57) (011), 3.437 (59) (020), 3.058 (43) (003), 2.918 (50) (2¯11), 2.795 (35) (013) and 2.753 (50) (121, 201). The crystal structure was solved based on single-crystal X-ray diffraction data,R1= 5.71%. The structure of antofagastaite consists of ordered and disordered blocks and is related to syngenite K2Ca(SO4)2·H2O. Incorporation of additional H2O molecules in the syngenite-type structure results in disorder of the one of the two tetrahedral sulfate groups occurring in antofagastaite. In addition to the above-reported type material, antofagastaite together with syngenite and blödite occurs in the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia.

The new mineral anatolyite Na6(Ca,Na)(Mg,Fe3+)3Al(AsO4)6 was found in the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. It is associated with potassic feldspar, hematite, tenorite, cassiterite, johillerite, tilasite, ericlaxmanite, lammerite, arsmirandite, sylvite, halite, aphthitalite, langbeinite, anhydrite, wulffite, krasheninnikovite, fluoborite, pseudobrookite and fluorophlogopite. Anatolyite occurs as aggregates (up to 2 mm across) of rhombohedral–prismatic, equant or slightly elongated along [001] crystals up to 0.2 mm. The mineral is transparent, pale brownish–pinkish, with vitreous lustre. It is brittle, cleavage was not observed and the fracture is uneven. The Mohs’ hardness is ca 4½. Dcalc is 3.872 g cm–3. Anatolyite is optically uniaxial (–), ω = 1.703(4) and ε = 1.675(3). Chemical composition (wt.%, electron microprobe) is: Na2O 16.55, K2O 0.43, CaO 2.49, MgO 5.80, MnO 0.16, CuO 0.69, ZnO 0.55, Al2O3 5.01, Fe2O3 7.94, TiO2 0.18, SnO2 0.17, SiO2 0.04, P2O5 0.55, As2O5 60.75, SO3 0.03, total 101.34. The empirical formula based on 24 O apfu is (Na5.90K0.10)Σ6.00(Ca0.50Na0.13Zn0.08Mn0.03)Σ0.74(Mg1.63Fe3+1.12Al0.15Cu0.10)Σ3.00(Al0.96Ti0.03Sn0.01)Σ1.00(As5.97P0.09Si0.01)Σ6.07O24. Anatolyite is trigonal, R$\bar{3}$c, a = 13.6574(10), c = 18.2349(17) Å, V = 2945.6(4) Å3 and Z = 6. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 7.21(33)(012), 4.539(16)(113), 4.347(27)(211), 3.421(20)(220), 3.196(31)(214), 2.981(17)(223), 2.827(100)(125) and 2.589(18)(410). The crystal structure was solved from single-crystal XRD data to R = 4.77%. The structure is based on a 3D heteropolyhedral framework formed by M4O18 clusters [M1 = Al and M2 = (Mg,Fe3+)] linked with AsO4 tetrahedra. (Ca,Na) and Na cations centre A1O6 and A2O8 polyhedra in voids of the framework. Anatolyite is isostructural with yurmarinite. The new mineral is named in honour of the outstanding Russian crystallographer, mineralogist and mathematician Anatoly Kapitonovich Boldyrev (1883–1946).

Two new isostructural minerals udinaite and arsenudinaite with the end-member formulae NaMg4(VO4)3 and NaMg4(AsO4)3, respectively, are found in the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. They are associated with one another and anhydrite, diopside, hematite, schäferite, berzeliite, svabite, calciojohillerite, tilasite, reznitskyite, ludwigite, rhabdoborite-group borates, forsterite, magnesioferrite, fluorapatite, pliniusite, and powellite. Both minerals occur as equant tetragonal prismatic–dipyramidal crystals up to 0.15 mm, aggregates up to 1 cm and interrupted crusts up to 2 × 2 cm2. Udinaite and arsenudinaite, visually indistinguishable from one another, are transparent, beige or brownish-yellowish, with vitreous lustre. Both minerals are optically uniaxial (–); ω = 1.785/1.777 and ε = 1.830/1.820, Dcalc. = 3.613/3.816 g·cm−3 (udinaite/arsenudinaite). The empirical formulae are: udinaite: (Na0.55Ca0.16)Σ0.71(Mg4.04Mn0.02Fe0.01)Σ4.07(V1.63As1.05P0.28Si0.03S0.01)Σ3.00O12; arsenudinaite: (Na0.57Ca0.13)Σ0.70(Mg4.01Mn0.01Fe0.01)Σ4.03(As2.07V0.84P0.10Si0.01S0.01)Σ3.03O12. Both minerals are tetragonal, I-42d, Z = 4, a = 6.8011(2)/6.8022(1), c = 19.1839(12)/19.1843(6) Å, and V = 887.35(7)/887.66(4) Å3, R1 = 0.0287/0.0119 (udinaite/arsenudinaite). Their crystal structure consists of the helical chains of edge-sharing MgO6 octahedra and isolated TO4 tetrahedra, forming a heteropolyhedral pseudo-framework with Na cations located in cavities. Both minerals are isostructural to jeffbenite. Udinaite and arsenudinaite form an isomorphous series in which the contents of T constituents vary within (in apfu): V1.6–0.1As2.8–1.0P0.4–0.0.

A new alluaudite-group mineral zincobradaczekite, a Zn–Cu ordered highly zincian analogue of bradaczekite, was discovered in sublimates of the Yadovitaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with bradaczekite, lammerite, lammerite-β, borisenkoite, mcbirneyite, sanidine, hematite, tenorite, pseudolyonsite, lyonsite, starovaite, rutile, tripuhyite, pseudobrookite, piypite, langbeinite, calciolangbeinite, aphthitalite, alumoklyuchevskite, and palmierite. Zincobradaczekite forms oblique-angled prismatic crystals up to 0.02 × 0.02 × 0.08 mm3 and equant or tabular crystals up to 0.05 mm. It is transparent, blue, greenish-blue, grey-blue or bluish-grey. The lustre is vitreous. Dcalc is 4.71 g cm−3. Zincobradaczekite is optically biaxial (–), α 1.786(5), β 1.846(8), γ 1.90(1), 2Vmeas. 80(5)o. Chemical composition (wt%, electron microprobe) is Na2O 4.07, K2O 0.53, CaO 0.01, MgO 0.71, MnO 0.01, CuO 19.89, ZnO 24.21, Al2O3 0.02, Fe2O3 0.90, TiO2 0.03, P2O5 0.41, V2O5 1.05, As2O5 47.10, SO3 1.01, and total 99.95. The empirical formula based on 12 O apfu is Na0.90K0.08Cu1.70Mg0.12Zn2.03Fe3+0.08(As2.79S0.09V0.08P0.04)Σ3.00O12. The simplified chemical formula is NaCu2Zn2(AsO4)3. Zincobradaczekite is monoclinic, C2/c, a 12.0375(13), b 12.4500(13), c 7.2213(8) A, β 117.506(7)o, V 959.90(18) A3 and Z 4. The strongest reflections of the powder XRD pattern [d,A(I)(hkl)] are 6.21(31)(020), 3.416(70)(310, − 112), 3.200(17)(002), 2.779(23)(− 402), 2.691(100)(− 132, 240), 1.841(20)(152) and 1.680(14)(− 642). The crystal structure was solved (single-crystal XRD, R = 4.38%). The simplified crystal chemical formula is A(1)□A(1)ʹCuA(2)□A(2)ʹNaM(1)CuM(2)Zn2(AsO4)3 (□—vacancy) and the end-member formula is NaCuCuZn2(AsO4)3. Zincobradaczekite and bradaczekite, ideally NaCuCuCu2(AsO4)3, are isostructural. In the Yadovitaya fumarole, Mg-poor bradaczekite forms an isomorphous series with zincobradaczekite, whilst in the neighbouring Arsenatnaya fumarole only a Zn-depleted and Mg-enriched variety of bradaczekite occurs. Zincobradaczekite and bradaczekite differ from other anhydrous alluaudite-group arsenates by increased values of the c and β unit-cell parameters due to the strong Jahn–Teller distortion of M(1)O6 octahedron predominantly occupied with Cu2+.

Polyoxometalate (POM) chemistry is an important avenue of comprehensive chemical research, due to the broad chemical, topological and structural variations of multinuclear polyoxoanions that result in advanced functionality of their derivatives. The majority of compounds in the polyoxometalate kingdom are synthesized under laboratory conditions. However, Nature has its own labs with the conditions often unconceivable to the mankind. The striking example of such a unique environment is volcanic fumaroles – the natural factories of gas-transport synthesis. We herein report on the discovery of a novel class of complex polyoxocuprates grown in the hot active fumaroles of the Tolbachik volcano at the Kamchatka Peninsula, Russia. The cuboctahedral nanoclusters {[MCu12O8](AsO4)8} are stabilized by the core Fe(III) or Ti(IV) cations residing in the unique cubic coordination. The nanoclusters are uniformly dispersed over the anion- and cation-deficient NaCl matrix. Our discovery might have promising implications for synthetic chemistry, indicating the possibility of preparation of complex polyoxocuprates by chemical vapor transport (CVT) techniques that emulate formation of minerals in high-temperature volcanic fumaroles.

A new tsumcorite-group mineral, nickeltsumcorite, Pb(Ni,Fe3+)2(AsO4)2(H2O,OH)2, the Ni-dominant analogue of tsumcorite and cobalttsumcorite, was found in the oxidation zone of a hydrothermal orebody containing gersdorffite and galena at the Km-3 mine, Lavrion, Attikí Prefecture, Greece. It is associated with annabergite, nickellotharmeyerite, nickelaustinite, gaspéite, calcite, dolomite, aragonite, quartz, goethite, cerussite, arseniosiderite, mimetite, oxyplumboroméite and Mn oxides/hydroxides. Nickeltsumcorite occurs as open-work aggregates and interrupted crusts up to 3 mm × 5 mm in area and up to 0.2 mm thick. They typically consist of coarse radial spherulites or dense concentric nodules up to 0.15 mm in diameter. Bunches or hemispherical clusters of crude individuals and separate imperfect, elongated crystals (up to 0.02 mm long) are also observed. Nickeltsumcorite is yellow, brownish-yellow, light brown or brown, with a yellow streak and a vitreous lustre. The Mohs hardness is ∼4. The mineral is brittle; one direction of distinct cleavage is observed under the microscope. D(calc.) = 5.02 g cm–3. Nickeltsumcorite is optically biaxial (–), α = 1.82(2), β = 1.87(1), γ = 1.90(1), 2V(obs.) is large. The chemical composition (wt.%, electron-microprobe data, H2O by difference) is CaO 2.79, PbO 28.12, MgO 0.30, CoO 0.15, NiO 17.39, ZnO 0.76, Mn2O3 0.57, Fe2O3 6.83, As2O5 38.17, H2O 4.92, total 100.00. The empirical formula, calculated based on 10 O apfu, is (Pb0.76Ca0.30)∑1.06(Ni1.39Fe3+0.51Zn0.06Mn3+0.04 Mg0.04Co0.01)∑2.05As1.99O7.97[(H2O)1.25(OH)0.78]. The strongest reflections in the powder X-ray diffraction pattern [d,Å(I)(hkl)] are 4.64 (100) (1̄11), 4.47 (41)(2̄01), 3.238 (82)(1̄12), 3.008(60)(201), 2.859(41)(021), 2.545(79)(3̄12, 112), 2.545 (79)(3̄12, 112) and 2.505 (61)(220, 2̄03). The cation composition, powder Xray diffraction data and IR spectrum show that nickeltsumcorite belongs to the tsumcorite structure type. The new mineral is monoclinic, space group C2/m, a = 9.124(8), b = 6.339(3), c = 7.567(7) Å, β = 115.19(6)°, V = 396.0(7) Å3 and Z = 2. Nickeltsumcorite forms a solid-solution series with nickellotharmeyerite.

A Ba-dominant (Ba > K) analogue of hydrodelhayelite (BDAH) from Lohley (Eifel Mts., Rhineland-Palatinate, Germany) and Ba-enriched varieties of related double- and triple-layer phyllosilicates from Eifel are studied. The crystal structure of BDAH was solved by direct methods and refined to R = 0.0698 [1483 unique reflections with I > 2σ(I)]. It is orthorhombic, Pmmn, a = 23.9532(9), b = 7.0522(3), c = 6.6064(3) A, V = 1115.97(8) A3, Z = 2. The structure is based upon delhayelite-type double-layer tetrahedral blocks [(Al,Si)4Si12O34(OH,O)4] connected by chains of (Ca,Fe)-centered octahedra. Ba2+ and subordinate K+ occur at partially vacant sites in zeolitic channels within the tetrahedral blocks. The crystal-chemical formula of BDAH is: (Ba0.42K0.34□0.24)(Ca0.88Fe0.12)2(□0.90Mg0.10)2[Si6(Al0.5Si0.5)2O17(OH0.71O0.29)2]⋅6H2O. The formation of BDAH and Ba-rich varieties of altered delhayelite/fivegite, gunterblassite and hillesheimite is considered as a result of leaching of Na, Cl, F and, partially, K and Ca accompanied with hydration and the capture of Ba as a result of natural ion exchange. These minerals are structurally a “bridge” between single-layer phyllosilicates and zeolites having the open three-dimensional tetrahedral Al-Si-O frameworks.

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 (Cu0.831Zn0.100Mg0.043Ni0.022)Σ0.996(Fe3+1.725Al0.219Mn3+0.048Ti0.008)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: (Cu0.619Zn0.422)Σ1.041(Al1.523Fe3+0.443Cr0.007)Σ1.973O4. The mineral is cubic, Fd-3m, a = 8.093(9) Å, V = 530.1(10) Å3. 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).

A new mineral, hilarionite, ideally Fe 2 3+ (SO4)(AsO4)(OH) · 6H2O, has been found in the Hilarion Mine, Agios Konstantinos, Kamariza, Lavrion district, Attiki Prefecture, Greece. It was formed in the oxidation zone of a sulfide-rich orebody in association with goethite, gypsum, bukovskyite, jarosite, melanterite, chalcanthite, allophane, and azurite. Hilarionite occurs as light green (typically with an olive or grayish tint) to light yellowish green spherulites (up to 1 mm in size) and bunches of prismatic to acicular “individuals” up to 0.5 mm long that are in fact near-parallel or divergent aggregates of very thin, curved fibers up to 0.3 mm long and usually lesser than 2 μm thick. The luster is silky to vitreous. The Mohs’ hardness is ca. 2. Hilarionite is ductile, its “individuals” are flexible and inelastic; fracture is uneven or splintery. D(meas) = 2.40(5), D(calc) = 2.486 g/cm3. IR spectrum shows the presence of arsenate and sulfate groups and H2O molecules in significant amounts. The Mossbauer spectrum indicates the presence of Fe3+ at two six-fold coordinated sites and the absence of Fe2+. Hilarionite is optically biaxial (+), α = 1.575(2), γ = 1.64(2), 2V is large. The chemical composition (electron microprobe, average of 7 point analyses; H2O determined by modified Penfield method) is as follows, wt %: 0.03 MnO, 0.18 CuO, 0.17 ZnO, 33.83 Fe2O3, 0.22 P2O5, 18.92 As2O5, 22.19 SO3, 26.3 H2O, total is 101.82%. The empirical formula calculated on the basis of 15 O is: (Fe 1.90 3+ Cu0.01Zn0.01)Σ1.92[(SO4)1.24(AsO4)0.74(PO4)0.01]Σ1.99(OH)1.01 · 6.03H2O. The X-ray powder diffraction data show close structural relationship of hilarionite and kaňkite, Fe 2 3+ (AsO4)2 · 7H2O. Hilarionite is monoclinic, space group C2/m, Cm or C2, a = 18.53(4), b = 17.43(3), c = 7.56(1) A, β = 94.06(15)°, V = 2436(3) A3, Z = 8. The strongest reflections in the X-ray powder diffraction pattern (d, A-I[hkl]) are: 12.66–100[110], $$7.60 - 6[00\bar 1]$$ , 5.00–10[22l], $$4.70 - 10[31\bar 1]$$ , 4.33–7[040]. Hilarionite is named after its type locality.

The crystal structures of cation-exchanged forms of hilairite obtained at 90°C (Pb- and Rb- exchanged samples (Pb0.60Na0.40H0.40ZrSi3O9 ∙ 3H2O [R32, a = 10.4718(3) A, c = 7.9392(2) A] and Rb1.48Na0.45H0.07ZrSi3O9 ∙ 0.53H2O[R3, a = 10.4743(4) A, c= 15.5433(8) A]) and at 150°C (K- and Cs-exchanged samples K1.81Na0.09H0.10ZrSi3O9 [R3, a = 10.3804(2) A, c = 14.9541(6) A] and Na1.14Cs0.55H0.31ZrSi3O9 ∙ 0.90H2O [R32, a = 10.5472(4) A, c = 15.8797(7) A]) were studied by X-ray dif- fraction. Their structures are based on a framework composed of helical chains [Si3O9]8 and isolated Zr octahedra. Relationships were found between the characteristics of exchange cations and the temperature of the ion exchange, on the one hand, and the compositional and structural features of the products, such as the type and degree of distortion of the framework and the concentration and arrangement of exchange cations and residual Na, and H2O molecules, on the other hand. The affinity of hilairite for extraframework cations in the ion exchange was shown to decrease in the order K → Rb → Pb → Ba → Sr → Ca → Cs.

Cation-exchange properties of natural hilairite, Na 2 {ZrSi 3 O 9 }· 3H 2 O, in aqueous salt solutions at 150 °C and the crystal structures of its Rb-, Ca-, Sr-, Ba- and Pb-exchanged forms have been studied on single crystals. All studied samples retain the mixed framework of “parent” hilairite consisting of helical chains [Si 3 O 9 ] ∞ linked by isolated [ZrO 6 ] octahedra. The main differences between the crystal structures of these cation-exchanged forms of hilairite and other representatives of the hilairite group are connected with the number and positions of extra-framework cations and water molecules, framework distortion, unit-cell dimensions and space-group symmetry. The single-crystal structure refinements (X-ray diffraction data) gave the following structural formulas for the studied samples: Rb 1.80 Na 0.20 Zr[Si 3 O 9 ]·0.4H 2 O for Rb-exchanged hilairite ( R 3, a = 10.477(1), c = 15.377(2) A, R 1( F ) = 3.35% for 2771 reflections with F o > 4σ( F o )), Ba 0.96 H 0.08 Zr[Si 3 O 9 ]·3H 2 O ( R 3, a = 20.976(3), c = 7.857(2) A, R 1( F ) = 4.96% for 4921 reflections with F o > 4σ( F o )) and SrZr[Si 3 O 9 ]·1.5H 2 O ( R 3, a = 20.964(3), c = 7.836(2) A, R 1( F ) = 10.23% for 3598 reflections with F o > 4σ( F o )) for Ba- and Sr-exchanged hilairites, respectively, and Ca 0.83 H 0.34 Zr[Si 3 O 9 ]·3H 2 O ( R 3, a = 10.456(1), c = 7.995(2) A, R 1( F ) = 2.63% for 1477 reflections with F o > 4σ( F o )) and Pb 0.82 Na 0.18 H 0.18 Zr[Si 3 O 9 ]·2.9H 2 O ( R 3, a = 10.477(1), c = 7.994(2) A, R 1( F ) = 2.21% for 1165 reflections with F o > 4σ( F o )) for Ca- and Pb-exchanged hilairites, respectively. All samples were twinned by merohedry and, except the Ca-exchanged sample, also racemically. The results of this study strongly indicate that natural cation-exchange processes can affect hilairite-group minerals under late-hydrothermal conditions.

The crystal structure of a Pb-exchanged form of zorite is studied by X-ray diffraction: Pb3.95(Ca0.1Sr0.05)[Ti(Ti0.80Nb0.20)4Si12O38(OH)] · 9.52H2O (sp. gr. Cmmm, R = 0.0530 for 680 independent reflections). The structure retains the mixed polyhedral framework of zorite, Na6[Ti(Ti,Nb)4(Si6O17)2(O,OH)5] · 11H2O. This framework is composed of xonotlite-like [Si6O17] ribbons linked to each other by columns of vertex-sharing (Ti,Nb)O6 octahedra and isolated TiO5 half-octahedra. Lead atoms in the Pb-exchanged form occupy one site, unlike Cs cations in the Cs-exchanged form of zorite, which are strongly disordered and partially occupy eight positions. The position of Pb2+ cations corresponds to the Na(2) position in the zorite structure, the Sr position in the Sr-exchanged form of ETS-4, and the K position in the K-exchanged form and is similar to the position of the water molecule W(3) in the structure of the Cs-exchanged form of zorite.

The crystal structures of K-and Cs-exchanged forms of zorite were studied by X-ray diffraction and IR spectroscopy: K4.75Na1.82[Ti(Ti0.79Nb0.20)4Si12O34(O,OH)5.2] × 10.62 H2O (sp. gr. Cmmm, R= 0.0481 for 516 independent reflections) and Cs4.34Na1.90[Ti(Ti0.80Nb0.18)4Si12O34(O,OH)5] × 5.37 H2O (sp. gr. Cmmm, R = 0.0285 for 621 independent reflections). Both structures retain the mixed polyhedral framework of zorite: Na6Ti(Ti,Nb)4(Si6O17)2(O,OH)5 × nH2O, where n ∼ 11. It is shown that the positions of the atoms located in the cavities of the frameworks of these compounds differ from those in the structures of zorite and its synthetic analogs.

Hilairite, Na2ZrSi3O9·3H2O, is a trigonal (space group R32) zeolite-like zirconosilicate. Its structure is based on the heteropolyhedral framework consisting of isolated [ZrO6] octahedra and helical chains [Si3O9]∞. Zeolitic cavities are occupied by Na+ cations and H2O molecules (Ilyushin et al. 1981; Grigorieva et al. 2009). Hilairite is one of the most wide-porous natural zirconosilicates. The experimental data showed that the mineral has strong ion-exchange properties with different large cations (Turchkova et al. 2006). In this work we study the dependence of crystal-chemical characteristics of its cation-exchanged forms (basing on K and Rb forms) on temperature of ion exchange.

Delhayelite, ideally K4Na2Ca2[AlSi7O19]F2Cl, is a mineral showing structural features of both phyllosilicates and silicates with heteropolyhedral frameworks. Its crystal structure is based upon the two-layer tetrahedral blocks, or double layers, [(Al,Si)4Si12O38], linked by the columns of edge-shared Ca-centered octahedra (Cannillo et al. 1969; Pekov et al. 2009). As it is shown in (Pekov et al. 2011), these two main building units form a heteropolyhedral quasi-framework with zeolite-like channels of two types: (1) inside the tetrahedral blocks, hosting K+ and Cl-; (2) in the interlayer space, between Ca columns, hosting Na+ and F-. Such ordering of three large cations and two halogen anions is a feature of delhayelite making it unique among minerals.

Many minerals show the properties commonly named “zeolitic”: ion exchange and leaching, sorption of gases and organic molecules, reversible hydration, etc. The most well-known examples are aluminosilicate zeolites, clay minerals and pyrochlores. Besides them, several other large groups of minerals are now in focus of research as potential microporous materials or their prototypes. First, there are Ti-, Zr-, Nb-silicates with heteropolyhedral frameworks. This paper is devoted to other minerals of this interest. There are two related families of natural silicates with structures based on Si,O or Al,Si,O tetrahedral layers and columns of edge-shared Ca-centered octahedra.

The ion exchange phenomenon is well-known for crystalline materials including minerals. It has been confirmed experimentally that many microporous minerals representing different chemical classes are capable of cation exchange with salt solutions, including dilute ones, even under room conditions. No doubt that microporous minerals show ion-exchange properties also in nature. Numerous works are devoted to the experimental study and practical use of ion-exchange properties of minerals, especially microporous aluminosilicates (zeolites, clay minerals, etc.), whereas reactions and products of natural ion exchange were almost non-studied to recent time.

The crystal structures of potassium-exchanged forms of catapleiite and hilairite of the compositions (K0.49Ca0.42Na0.26)ZrSi3O9 · 2[(H2O)0.8(H3O)0.2] and K0.51ZrSi3O9 · 3[(H2O)0.5K0.27(H3O)0.23], respectively, were studied by X-ray diffraction and IR spectroscopy. Both structures retain the heteropolyhedral frameworks of the parent minerals formed by Zr octahedra and Si tetrahedra. The K cations occupy different positions in these minerals. In K-exchanged catapleiite, K cations are located only in the position occupied by Na in the structure of the parent mineral. In the K-exchanged form of hilairite, K cations are not only involved in the Na position but also partially occupy the H2O position.