Hydroxylbastnäsite-(La), the OH- and La-dominant member of the bastnäsite group, in fact known for many years, was studied in detail and has been approved by the IMA–CNMNC as a new mineral species with the ideal, end-member formula La(CO3)(OH). The holotype originates from the Vuoriyarvi (another spelling: Vuorijärvi) alkaline-ultrabasic complex, Northern Karelia, and the cotype from the Mochalin Log REE deposit, Potaniny Mts, South Urals, both in Russia. At Vuoriyarvi, hydroxylbastnäsite-(La) occurs as clusters (up to 1 mm) of light brown, honey-yellow or colourless hexagonal tabular to short-prismatic crystals up to 0.15 mm associated with fluorite and ancylite-(Ce) in cavities of calcite–dolomite carbonatites. At Mochalin Log, hydroxylbastnäsite-(La) forms light brown grains up to 0.2 mm included in massive aggregates of other LREE minerals: bastnäsite-(Ce), bastnäsite-(La), percleveite-(Ce), percleveite-(La), biraite-(Ce), biraite-(La), törnebohmite-(La), ferriperbøeite-(Ce), allanite-(Ce), etc. Dmeas is 4.75(2) and Dcalc is 4.778 g cm–3 (holotype). Hydroxylbastnäsite-(La) is optically uniaxial (+), ω = 1.76(1) and ε = 1.86(1) (holotype). The chemical composition (wt.%, electron microprobe, CO2 and H2O calculated: holotype/cotype) is: CaO 0.23/0.00, SrO 0.07/0.00, La2O3 39.47/39.58, Ce2O3 33.51/31.99, Pr2O3 1.03/1.51, Nd2O3 1.95/2.38, F 0.76/3.33, CO2 20.49/20.34, H2O 3.77/2.58, –O=F 0.32/1.40, total 100.96/100.31. The empirical formulae, calculated based on the sum of metal cations of 1 apfu and one CO3 group pfu, are (La0.52Ce0.44Nd0.02Pr0.01Ca0.01)Σ1.00(CO3)[(OH)0.90F0.09]Σ0.99 (holotype) and (La0.53Ce0.42Nd0.03Pr0.02)Σ1.00(CO3)[(OH)0.62F0.38]Σ1.00 (cotype). Hydroxylbastnäsite-(La) is hexagonal, P6̅, unit-cell parameters (from powder XRD data, holotype/cotype) are: a = 12.537(3)/12.533(1), c = 9.968(2)/9.908(1) Å, V = 1356.8(5)/1347.9(3) Å3 and Z = 18. Strong reflections of the powder XRD pattern [d,Å(I)(hkl)] are (holotype): 4.98(39)(002), 3.616(88)(300), 2.926(100)(302), 2.089(41)(330), 2.052(46)(304) and 1.927(40)(332). The crystal structure of holotype hydroxylbastnäsite-(La) was refined by the Rietveld method, Rwp = 0.0071, Rp = 0.0050, Robs = 0.0466. It is isostructural to hydroxylbastnäsite-(Ce) and synthetic bastnäsite-type hydroxyl-carbonates REE3+(CO3)(OH) (REE = La–Er), but differs from fluorine-dominant bastnäsites which adopt the space group P6̅2c.

In terrestrial rocks, Br minerals are extremely rare with only nine minerals known where Br is a dominant component. A new arsenite bromide mineral ermakovite, (NH4)(As2O3)2Br, was discovered at the tract of Kukhi-Malik, Fan-Yagnob coal deposit, ca. 75 km N of Dushanbe, Tajikistan. Ermakovite is a fumarolic mineral formed directly from gas from a natural underground coal fire. Associated minerals are sulfur, realgar, amorphous As-sulfides, salammoniac, alacránite, bonazziite and thermessaite-(NH4). In addition, there are amorphous As2S3 intergrowths associated with ermakovite. The mineral typically occurs as tabular or prismatic hexagonal crystals up to 200 μm with the following forms: c (001), m (010) and p (014). Spherulites and multi-twinned intergrowths are very common. The mineral is optically uniaxial (–), ω = 1.960 (5) and ɛ = 1.716(3) (589 nm). The measured density is 3.64(2) g/cm3. The mineral is insoluble in water, HCl, HNO3 and organic solvents. The empirical formula calculated on the basis of (As+Sb) = 4 atoms per formula unit is [(NH4)0.92Na0.01]0.93(As3.94Sb0.06)4.00O6.02(Br0.97Cl0.08I0.01)1.06. The strongest lines in the powder X-ray diffraction pattern are [d, Å (I, %) (hkl)]: 9.160 (80)(001); 4.560(90)(002); 3.228(100) (102); 2.629(80)(110); and 2.522(60)(103). Ermakovite is hexagonal, P6/mmm, a = 5.271(3), c = 9.157(6) Å, V = 220.3(3) Å3 and Z = 1. The sandwich-type structure of ermakovite is based on three types of layers: (1) a honeycomb [As2O3] arsenite layer; (2) an NH4+ layer; and (3) a Br layer. The layer stacking sequence is ⋅⋅⋅NH4–As2O3–Br–As2O3–NH4⋅⋅⋅. Ermakovite has a synthetic analogue. Infrared and Raman spectra are also reported.

An overview of the processes that give rise to high concentrations of Br, leading to the formation of exotic Br minerals, is given.

Nickolayite, FeMoP, is a new terrestrial phosphide structurally related to allabogdanite (high-pressure modification of (Fe,Ni)2P), and the meteoritic phosphides florenskyite, FeTiP and andreyivanovite, FeCrP. From the point of view of chemical composition, nickolayite is an Fe-analogue of monipite, MoNiP. The mineral was discovered in the Daba-Siwaqa complex, Central Jordan, a part of the pyrometamorphic Hatrurim Formation (the Mottled Zone), whose outcrops encompass a 150 × 200 km area around the Dead Sea in the Middle East. Nickolayite appears as an accessory phase in the fused clinopyroxene–plagioclase rocks texturally resembling gabbro–dolerite. The irregularly shaped grains of the mineral, up to 80 μm in size are associated with baryte, tridymite, chromite, hematite, pyrrhotite, fluorapatite, titanite and powellite. Macroscopically, nickolayite grains possess light-grey to greyish-white colour and metallic lustre. The mineral is ductile. The mean VHN hardness (50 g load) is 538 kg mm–2. The calculated density based on the empirical formula and the unit-cell parameters is 7.819 g cm–1. In reflected light, nickolayite has a white colour, with no bireflectance or pleochroism. The COM approved reflectance values [Rmax/Rmin (%), λ(nm)] are: 48.5/46.5 (470), 50.5/48.5 (546), 51.8/49.9 (589) and 53.9/52.0 (650). The chemical composition of the holotype crystal is (electron microprobe, average of 4 analyses, wt.%): Fe 32.21, Mo 47.06, Ni 3.69, Co 0.13, P 17.45, total 100.54, that corresponds to the empirical formula Fe1.00(Mo0.87Ni0.11Fe0.02)Σ1.00P1.00 and an ideal formula of FeMoP. Nickolayite is orthorhombic, space group Pnma, unit-cell parameters of holotype material are: a = 5.9519(5), b = 3.7070(3), c = 6.8465(6) Å, V = 151.06(2) Å3 and Z = 4. The crystal structure of holotype material was solved and refined to R1 = 0.0174 based on 251 unique observed reflections. The origin of the mineral is probably connected to the processes of co-reduction of molybdenum- and phosphorus-bearing minerals during high-temperature pyrometamorphic processes.

We report the crystal structures of eight new synthetic multinary Rb–Cu sulfates representing four new structure types: δ-Rb2Cu(SO4)2, γ-RbNaCu(SO4)2, γ-RbKCu(SO4)2, Rb2Cu2(SO4)3, Rb2Cu2(SO4)3(H2O), β-Rb2Cu(SO4)Cl2, β-Rb4Cu4O2(SO4)4⋅(Cu0.83Rb0.17Cl) and Rb2Cu5O(SO4)5. The determination of their crystal structures significantly expands the family of anhydrous copper sulfates. Some of the anhydrous rubidium copper sulfates obtained turned out to be isostructural to known compounds and minerals. Rb2Cu5O(SO4)5 is isostructural to cesiodymite, CsKCu5O(SO4)5 and cryptochalcite, K2Cu5O(SO4)5. Rb2Cu2(SO4)3 also shows an example of crystallisation in the already known structure type first observed for synthetic K2Cu2(SO4)3. ‘Hydrolangbeinite’, Rb2Cu2(SO4)3(H2O), was formed as a result of a minor hydration of the initial mixture of reagents.

The minerals and synthetic framework compounds of the A2Cu(SO4)2 series demonstrate a vivid example of morphotropism with the formation of structural types depending on the size of the cations residing in the cavities of the [Cu(SO4)2]2– open framework. To date, five types (α, β, γ, δ and ε) can be distinguished. We propose to call this series of compounds ‘saranchinaite-type’, as the stoichiometry A2Cu(SO4)2 was first encountered during the discovery and description of saranchinaite, Na2Cu(SO4)2.

The discovery of β-Rb2Cu(SO4)Cl2, a new monoclinic polymorph of chlorothionite, seems to be of particular interest considering the recently discovered interesting magnetic properties of synthetic K2Cu(SO4)X2 (X = Cl and Br) and Na2Cu(SO4)Cl2.

In these new structural architectures, a number of features have been revealed that were seldom observed previously. The first is the bidentate coordination of the sulfate tetrahedron via edge-sharing with the Cu2+-centred coordination polyhedron. Until recently, such coordination was known only for the chlorothionite structure. The second is formation of ‘high-coordinate’ CuO7 polyhedra. The structures of the new compounds suggest that such coordination is not in fact so uncommon, at least among anhydrous alkali copper sulfates. All of the described features clearly indicate the importance of further systematic studies of anhydrous copper-sulfate systems. Their exploration, particularly of the new copper-oxide substructures with new coordination environments, is highly likely to lead to new potentially interesting magnetic properties due to the unusual arrangements of magnetically active Cu2+ cations.

In addition to experimental details on the synthesis of rubidium analogues of anhydrous potassium and sodium sulfates, this work also provides an analysis and a brief review of the geochemistry of rubidium in volcanic environments.

The Quaternary carbonatite–nephelinite Kerimasi volcano is located within the Gregory rift in northern Tanzania. It is composed of nephelinitic and carbonatitic pyroclastic rocks, tuffs, tuff breccias and pyroclastic breccias, which contain blocks of different plutonic (predominantly ijolite) and volcanic (predominantly nephelinite) rocks including carbonatites. The plutonic and volcanic carbonatites both contain calcite as the major mineral with variable amounts of magnetite or magnesioferrite, apatite and forsterite. Carbonatites also contain accessory baddeleyite, kerimasite, pyrochlore and calzirtite. Zr and Nb minerals are rarely observed in rock samples, though they are abundant in eluvial deposits of carbonatite tuff/pyroclastic breccias in the Loluni and Kisete craters. Pyrochlore, ideally (CaNa)Nb2O6F, occurs as octahedral and cubo-octahedral crystals up to 300 μm in size. Compositionally, pyrochlore from Loluni and Kisete differs. The former is enriched in U (up to 19.4 wt.% UO2), light rare earth elements (up to 8.3 wt.% LREE2O3) and Zr (up to 14.4 wt.% ZrO2), and the latter contains elevated Ti (up to 7.3 wt.% TiO2). All the crystals investigated were crystalline, including those with high U content (a = 10.4152(1) Å for Loluni and a = 10.3763(1) Å for Kisete crystals). They have little or no subsolidus alteration nor low-temperature cation exchange (A-site vacancy up to 1.5% of the site), and are suitable for single-crystal X-ray diffraction analysis (R1 = 0.0206 and 0.0290; for all independent reflections for Loluni and Kisete crystals, respectively). Observed variations in the pyrochlore composition, particularly Zr content, from the Loluni and Kisete craters suggest crystallisation from compositionally different carbonatitic melts. The majority of pyrochlore crystals studied exhibit exceptionally well-preserved oscillatory- and sometimes sector-type zoning. The preferential incorporation of smaller and higher charged elements into more geometrically constrained sites on the growing surfaces explains the formation of the sector zoning. The oscillatory zoning can be rationalised by considering convectional instabilities of carbonatite magmas during their emplacement.

Exhalative mineral assemblages from fumaroles of Tolbachik volcano are very rich in anhydrous sulfate minerals of alkali and transition metals. Koryakite, ideally NaKMg2Al2(SO4)6, was found in the Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Koryakite occurs as a product of fumarolic activity and closely associates with euchlorine and langbeinite. Koryakite is trigonal, R$\bar{3}$, a = 8.1124(11), c = 22.704(7) Å and V = 1294.0(5) Å3. The chemical composition determined by electron-microprobe analysis is (wt.%): Na2O 4.27, K2O 5.85, ZnO 0.31, СaO 0.31, CuO 0.76, MgO 10.15, Al2O3 11.47, Fe2O3 2.73, SO3 64.33 and SiO2 0.13, total 100.31. The empirical formula calculated on the basis of 24 O apfu is Na1.03K0.93(Mg1.89Cu0.07Ca0.04Zn0.03)Σ2.03(Al1.68Fe3+0.26)Σ1.94(S6.02Si0.02)Σ6.04O24. No natural or synthetic chemical analogues of koryakite are known to date. The topology of the [M2+2M3+2(SO4)6]2– heteropolyhedral framework in koryakite is very similar to the one in millosevichite, Al2(SO4)3 and mikasaite, Fe3+2(SO4)3. Replacement of part of the trivalent cations in the [M3+2(SO4)3]0 framework by divalent cations gives the framework a negative charge for koryakite and allows the incorporation of the alkali species in the channels. This structural mechanism is reminiscent of the concept of stuffed derivative structures. Koryakite is also structurally related to synthetic NaMgFe3+(SO4)3 and to the broader family of NASICON-related phases.

A new mineral majzlanite, ideally K2Na(ZnNa)Ca(SO4)4, was found in high-temperature exhalative mineral assemblages in the Yadovitaya fumarole, Second scoria cone of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Majzlanite is associated closely with langbeinite and K-bearing thénardite. Majzlanite is grey with a bluish tint, has a white streak and vitreous lustre. The mineral is soluble in warm water. Majzlanite is monoclinic, C2/c, a = 16.007(2), b = 9.5239(11), c = 9.1182(10) Å, β = 94.828(7)°, V = 1385.2(3) Å3 and Z = 16. The eight strongest lines of the X-ray powder diffraction pattern are [d, Å (I, %)(hkl)]: 3.3721(40)($\bar{3}$12), 3.1473(56)($\bar{4}$02), 3.1062(65)($\bar{2}$22), 2.9495(50)($\bar{1}$31), 2.8736(100)($\bar{1}$13), 2.8350(70)(421), 2.8031(45)(511) and 2.6162(41)($\bar{5}$12). The following structural formula was obtained: K2Na(Zn0.88Na0.60Cu0.36Mg0.16)(Ca0.76Na0.24)(S0.98Al0.015Si0.005O4)4. The chemical composition determined by electron-microprobe analysis is (wt.%): Na2O 9.73, K2O 15.27, ZnO 11.20, CaO 7.03, CuO 4.26, MgO 1.07, Al2O3 0.47, SO3 51.34, SiO2 0.12, total 100.49. The empirical formula calculated on the basis of 16 O apfu is K1.99Na1.93Zn0.84Ca0.77Cu0.33Mg0.16(S3.94Al0.06Si0.01)O16 and the simplified formula is K2Na(Zn,Na,Cu,Mg)Σ2(Ca,Na)(SO4)4. No natural or synthetic compounds directly chemically and/or structurally related to majzlanite are known to date. The topology of the heteropolyhedral framework in majzlanite is complex. An interesting feature of the structure of majzlanite is an edge-sharing of ZnO6 octahedra with SO4 tetrahedra.

Dokuchaevite, ideally Cu8O2(VO4)3Cl3, was found in the Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Dokuchaevite occurs on the crusts of various copper sulfate exhalative minerals (such as kamchatkite and euchlorine) as individual prismatic crystals. Dokuchaevite is triclinic, P$\bar{1}$, a = 6.332(3), b = 8.204(4), c = 15.562(8) Å, α = 90.498(8), β = 97.173(7), γ = 90.896(13)°, V = 801.9(7) Å3 and R1 = 0.057. The eight strongest lines of the X-ray powder diffraction pattern are (d, Å (I)(hkl): (15.4396)(18)(00$\bar{1}$), (7.2762)(27)(0$\bar{1}$1), (5.5957)(43)(012), (4.8571)(33)($\bar{1}\bar{1}$1), (3.1929) (29)(023), (2.7915)(30)(202), (2.5645)(21)(032), (2.5220)(100)(1$\bar{3}$0), (2.4906)(18)(130) and (2.3267)(71)(2$\bar{2}$2). The chemical composition determined by electron-microprobe analysis is (wt.%): CuO 60.87, ZnO 0.50, FeO 0.36, V2O5 19.85, As2O5 6.96, SO3 0.44, MoO3 1.41, SiO2 0.20, P2O5 0.22, Cl 10.66, –O = Cl2 2.41, total 99.06. The empirical formula calculated on the basis of 17 anions per formula unit is (Cu7.72Zn0.06Fe0.05)Σ7.83(V2.20As0.61Mo0.10S0.06P0.03Si0.03)Σ3.03O13.96Cl3.04.

The crystal structure of dokuchaevite represents a new structure type with eight Cu sites, which demonstrate the remarkable diversity of Cu2+ mixed-ligand coordination environments. The crystal structure of dokuchaevite is based on OCu4 tetrahedra that share common corners thus forming [O2Cu6]8+ single chains. Two of the eight symmetrically independent copper atoms do not form Cu–O bonds with additional oxygen atoms, and thus are not part of the OCu4 tetrahedra, but provide the three-dimensional integrity of the [O2Cu6]8+ chains into a framework. TO4 mixed tetrahedral groups are located within the cavities of the framework. The structural formula of dokuchaevite can be represented as Cu2[Cu6O2](VO4)3Cl3.

Markhininite, ideally TlBi(SO4)2, was found in a fumarole of the 1st cinder cone of the North Breach of the Great Fissure Tolbachik volcano eruption (1975–1976), Kamchatka Peninsula, Russia. Markhininite occurs as white pseudohexagonal plates associated with shcherbinaite, pauflerite, bobjonesite, karpovite, evdokimovite and microcrystalline Mg, Al, Fe and Na sulfates. Markhininite is triclinic, P, a = 7.378(3), b = 10.657(3), c = 10.657(3) Å , α = 61.31(3), β = 70.964(7), γ = 70.964(7)º, V = 680.2(4) Å3, Z = 4 (from single-crystal diffraction data). The eight strongest lines of the X-ray powder diffraction pattern are (I/d/hkl): 68/4.264/111, 100/3.441/113, 35/3.350/222, 24/3.125/122, 23/3.054/202, 45/2.717/022, 20/2.217/331, 34/2.114/204. Chemical composition determined by electron microprobe analysis is (wt.%): Tl2O 35.41, Bi2O3 38.91, SO3 25.19, total 99.51. The empirical formula based on 8 O a.p.f.u. is Tl1.04Bi1.05S1.97O8. The simplified formula is TlBi(SO4)2, which requires Tl2O 35.08, Bi2O3 38.48, SO3 26.44, total 100.00 wt.%. The crystal structure was solved by direct methods and refined to R1 = 0.055 on the basis of 1425 independent observed reflections. The structure contains four Tl+ and two Bi3+ sites in holodirected symmetrical coordination. BiO8 tetragonal antiprisms and SO4 tetrahedra in markhininite share common O atoms to produce [Bi(SO4)2]– layers of the yavapaiite type. The layers are parallel to (111) and linked together through interlayer Tl+ cations. The mineral is named in honour of Professor Yevgeniy Konstantinovich Markhinin (b. 1926), Institute of Volcanology, Russian Academy of Sciences, Kamchatka peninsula, Russia, in recognition of his contributions to volcanology. Markhininite is the first oxysalt compound that contains both Tl and Bi in an ordered crystal structure.

Carbonatites from the Khibina Alkaline Massif (360–380 Ma), Kola Peninsula, Russia, contain one of the most diverse assemblages of REE minerals described thus far from carbonatites and provide an excellent opportunity to track the evolution of late-stage carbonatites and their sub-solidus (secondary) changes. Twelve rare earth minerals have been analysed in detail and compared with literature analyses. These minerals include some common to carbonatites (e.g. Ca-rare-earth fluocarbonates and ancylite-(Ce)) plus burbankite and carbocernaite and some very rare Ba,REE fluocarbonates.

Overall the REE patterns change from light rare earth-enriched in the earliest carbonatites to heavy rare earth-enriched in the late carbonate-zeolite veins, an evolution which is thought to reflect the increasing ‘carbohydrothermal’ nature of the rock-forming fluid. Many of the carbonatites have been subject to sub-solidus metasomatic processes whose products include hexagonal prismatic pseudomorphs of ancylite-(Ce) or synchysite-(Ce), strontianite and baryte after burbankite and carbocernaite. The metasomatic processes cause little change in the rare earth patterns and it is thought that they took place soon after emplacement.

The new mineral somersetite, has been found at Torr Works (‘Merehead quarry’) in Somerset, England, United Kingdom. Somersetite is green or white (typically it is similar visually to hydrocerussite-like minerals but with a mint-green tint), forms plates and subhedral grains up to 5 mm across and up to 2 mm thick. In bi-coloured crystals it forms very thin intergrowths with plumbonacrite. The empirical formula of somersetite is Pb8.00C5.00H4.00O20. The simplified formula is Pb8O(OH)4(CO3)5, which requires: PbO = 87.46, CO2 = 10.78, H2O = 1.76, total 100.00 wt.%.

The infrared spectrum of somersetite is similar to that of plumbonacrite and, to a lesser degree, hydrocerussite. Somersetite is hexagonal, P63/mmc, a = 5.2427(7), c = 40.624(6) Å, V = 967.0(3) Å3 and Z = 2. The eight strongest reflections of the powder X-ray diffraction (XRD) pattern [d,Å(I)(hkl)] are: 4.308(33)(103), 4.148(25)(104), 3.581(40)(107), 3.390(100)(108), 3.206(55)(109), 2.625(78)(110), 2.544(98)(0.0.16) and 2.119(27)(1.0.17). The crystal structure was solved from single-crystal XRD data giving R1 = 0.031. The structure of somersetite is unique and consists of the alternation of the electroneutral plumbonacrite-type [Pb5O(OH)2(CO3)3]0 and hydrocerussite-type [Pb3(OH)2(CO3)2]0 blocks separated by stereochemically active lone electron pairs on Pb2+. There are two blocks of each type per unit cell in the structure, which corresponds to the formula [Pb5O(OH)2(CO3)3][Pb3(OH)2(CO3)2] or Pb8O(OH)4(CO3)5 in a simplified representation. The 2D blocks are held together by weak Pb–O bonds and weak interactions between lone pairs.

Belousovite, ideally KZn(SO4)Cl, was found in a Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Belousovite occurs as irregularly-shaped grains and in the form of microcrystalline masses associated with kamchatkite, langbeinite, euchlorine, anglesite and zincite. Belousovite is monoclinic, P21/c, a = 6.8904(5), b = 9.6115(7), c = 8.2144(6) Å, β = 96.582(2), V = 540.43(7) Å3 and Z = 4 (from single-crystal diffraction data). The eight strongest lines of the powder X-ray diffraction pattern are [dmeas Å(I)(hkl)]: 6.8451(100)(100), (3.6401)(71)($\bar{1}$21), (3.1592)(84)(1$\bar{1}$2), (3.1218)(41)($\bar{2}$11), (3.1140)(52)(022), (2.9812)(41)(031), (2.9121)(44)(130) and (2.0483)(19)($\bar{3}$12). The chemical composition determined by the electron-microprobe analysis is (wt.%): K2O 19.55, Rb2O 0.58, ZnO 34.85, SO3 34.65, Cl 14.77, –O = Cl2 3.34, total 101.06. The empirical formula based on O + Cl = 5 apfu is K0.97Rb0.01Zn1.00S1.01O4.03Cl0.97. The simplified formula is KZn(SO4)Cl. The crystal structure was solved by direct methods and refined to R1 = 0.029 on the basis of 1965 independent observed reflections. The structure of belousovite consists of infinite [ZnSO4Cl]– layers and K+ ions. [ZnSO4Cl]– layers are formed by corner sharing mixed-ligand ZnO3Cl tetrahedra and SO4 tetrahedra. The topology of [ZnSO4Cl]– layers in belousovite is identical to [Si4O10]4– layers in the minerals of the apophyllite group. A review of mixed-ligand ZnOmCln coordination polyhedra in minerals and inorganic compounds is given.

The hydrocerussite-related phase, NaPb5(CO3)4(OH)3, has been found as colourless lamellar crystals in cavities within a pebble of the ancient marine slag collected in the Pacha Limani area of the Lavrion mining district, Attiki, Greece. This phase of anthropogenic origin was characterized by electron microprobe, infrared spectroscopy, powder and single-crystal X-ray diffraction. The unique crystal structure (P63/mmc, a = 5.2533(11), c = 29.425(6) Å, V = 703.3(3) Å3 and R1 = 0.047) is based upon structurally and chemically different electroneutral blocks. Each of the blocks can be split into separate sheets. The outer sheets in each block are topologically identical and have the composition [PbCO3]0. The [Pb(OH)2]0 lead hydroxide sheet is sandwiched between the two [PbCO3]0 sheets resulting in the formation of the first block [Pb3(OH)2(CO3)2]0 structurally and compositionally identical to that one in hydrocerussite Pb3(OH)2(CO3)2. Similarly the [Na(OH)]0 sheet is sandwiched between another two [PbCO3]0 sheets thus forming the [NaPb2(OH)(CO3)2]0 block described previously in the structure of abellaite NaPb2(OH)(CO3)2. Stereochemically active lone electron pairs on Pb2+ cations are located between the blocks. There are two blocks of each type per unit cell, which corresponds to the following formula: [Pb3(OH)2(CO3)2][NaPb2(OH)(CO3)2] or NaPb5(CO3)4(OH)3 in the simplified representation. The formation of NaPb5(CO3)4(OH)3 in Lavrion slags is by the contact of lead-rich slags with the sea water over the last two thousand years.