Four specimens of the roméite-group minerals oxyplumboroméite and fluorcalcioroméite from the Långban Mn-Fe deposit in Central Sweden were structurally and chemically characterized by single-crystal X-ray diffraction, electron microprobe analysis and infrared spectroscopy. The data obtained and those on additional roméite samples from literature show that the main structural variations within the roméite group are related to variations in the content of Pb2+, which is incorporated into the roméite structure via the substitution Pb2+→A2+ where A2+ = Ca, Mn and Sr. Additionally, the cation occupancy at the six-fold coordinated B site, which is associated with the heterovalent substitution BFe3+ + Y☐→BSb5++YO2-, can strongly affect structural parameters.

Chemical formulae of the roméite minerals group are discussed. According to crystal-chemical information, the species associated with the name ‘kenoplumboroméite’, hydroxycalcioroméite and fluorcalcioroméite most closely approximate end-member compositions Pb2(SbFe3+)O6☐, Ca2(Sb5+Ti) O6(OH) and (CaNa)Sb2O6F, respectively. However, in accord with pyrochlore nomenclature rules, their names correspond to multiple end-members and are best described by the general formulae: (Pb,#)2(Sb,#)2O6☐, (Ca,#)2(Sb,#)2O6(OH) and (Ca,#)Sb2(O,#)6F, where ‘#’ indicates an unspecified charge-balancing chemical substituent, including vacancies.

Polloneite, ideally AgPb46As26Sb23S120, is a new N = 4 member of the sartorite homologous series. It occurs in a matrix of baryte from the Pizzone level of the Pollone baryte-pyrite-(Pb-Zn-Ag) deposit at Valdicastello Carducci, near Pietrasanta, in the Apuan Alps, Tuscany, Italy, as anhedral grains up to 0.5 mm across. The mineral is opaque, greyish black with a metallic lustre. In reflected light polloneite is white, bireflectance is moderate. Internal reflections are absent. Under crossed polars, anisotropism is moderate with rotation tints in brown-violet and deep grey. The reflectance data (%, air) are: 30.2, 42.4 at 470 nm, 28.8, 41.0 at 546 nm, 27.9, 39.8 at 589 nm and 26.0, 37.4 at 650 nm. Mohs hardness is 3–3½, microhardness VHN50 exhibits a mean value of 200 kg mm-2. The average results of 15 electronmicroprobe analyses of three grains are Ag 0.71(5), Pb 52.05(21), As 10.61(22), Sb 15.40(12), S 21.16(8), total 99.92(15) wt.%, corresponding to Ag1.20Pb45.76As25.79Sb23.04S120.21 (on the basis of Me + S = 216 apfu). The simplified formula AgPb46As26Sb23S120 is in accordance with the results of a crystal structure determination. The calculated density is 5.77 g cm–3. Polloneite is monoclinic, space group P21, a = 8.413(2), b = 25.901(5), c = 23.818(5) Å, β = 90.01(3)°, V = 5189.8(18)Å3, Z = 1. The strongest eight lines in the calculated powder-diffraction pattern [d in Å(I)hkl] are 3.795(100)(026), 3.414(60)(233), 3.238(69)(080), 3.020(97)(253), 2.922(82)(066), 2.738(73)(236), 2.375(79)(290) and 2.103(64)(400). Polloneite is a new N = 4 member of the sartorite homologous series with substantial Sb and small, but important, Ag content. It is a three-fold superstructure with a tripled unit-cell parameter, 7.9 Å, of sartorite homologues. In the As-Sb rich slabs, several types of crankshaft chains and isolated (As,Sb)–S polyhedra occur. A sequence of three different, tightly bonded double-layer fragments (broad ribbons) contains two asymmetric fragments with long crankshaft chains whereas the third fragment type, with Ag, contains small mirror-symmetrical metalloid groups and no crankshaft chains. This configuration can potentially cause order-disorder phenomena in the structure. The threefold superstructure and the mixed As-Sb character distinguish polloneite from veenite and from dufrénoysite, respectively.

The Olympic Dam iron-oxide copper-gold-silver-uranium deposit, South Australia, contains three dominant U minerals: uraninite; coffinite; and brannerite. Microanalytical and petrographic observations provide evidence for an interpretation in which brannerite and coffinite essentially represent the products of U mineralizing events after initial deposit formation at 1.6 Ga. Marked compositional and textural differences between the various types of brannerite and coffinite highlight the role of multiple stages of U dissolution and reprecipitation.

On the basis of petrography (size, habit, textures and mineral associations) and compositional variation, brannerites are divided into four distinct groups (brannerite-A, -B, -C and -D), and coffinite into three groups (coffinite-A, -B and -C). Brannerite-A ranges in composition from what is effectively uraniferous rutile to stoichiometric brannerite, and has elevated (Mg +Mn + Na + K) and (Fe + Al) compared to other brannerite types. It displays the most diverse range of morphologies, including complex irregular-shaped aggregates, replacement bands, and discrete elongate seams. The internal structure of brannerite-A consists of randomly-oriented hair-like needles and blades. Brannerite-B (>5 μm in size) is generally prismatic and typically associated with baryte and REY minerals (REE+Y= REY). Brannerite-C and -D are both associated with Cu-(Fe)-sulfides and are typically composed of irregular masses and blebs (10–50 μm in size) with a more uniform or massive internal structure. Brannerite-D is distinct from -C and always contains inclusions of galena. Brannerite-B to -D all contain elevated ΣREY, with brannerite-B and -C having elevated As, and brannerite-D having elevated Nb.

All coffinite is typically globular (each globule is 2–10 μm in size) to collomorphic in appearance. Coffinite-A ranges from discrete globules to collomorphic bands completely encompassing quartz. Coffinite-B is always found with uraninite, and includes collomorph coffinite enveloped by massive uraninite, as well as aureoles of coffinite on the margins of uraninite crystals. Coffinite-C is associated with brannerite and REY minerals. The majority of coffinite is heterogeneous.

Brannerite and coffinite have probably precipitated as part of a late-stage hydrothermal U-event, which might have involved the dissolution and/or reprecipitation of earlier precipitated uraninite, or could represent the products of a later U mineralizing event. Evidence which supports formation of late-stage coffinite and brannerite includes: (1) low-Pb contents of both minerals; (2) coffinite is commonly found on the edges of uraninite, implying later deposition; and (3) coffinite is often found on the edge of brannerite aggregates, suggestive of brannerite precipitation occurred before coffinite. Moreover, there are many features (e.g. banding, scalloped edges, alteration rinds, variable compositions etc.) indicative of hydrothermal alteration processes.

Carbonatites are enriched in critical raw materials such as the rare-earth elements (REE), niobium, fluorspar and phosphate. A better understanding of their fluid regimes will improve our knowledge of how to target and exploit economic deposits. This study shows that multiple fluid phases penetrated the surrounding fenite aureole during carbonatite emplacement at Chilwa Island, Malawi. The first alkaline fluids formed the main fenite assemblage and later microscopic vein networks contain the minerals of potential economic interest such as pyrochlore in high-grade fenite and rare-earth minerals throughout the aureole. Seventeen samples of fenite rock from the metasomatic aureole around the Chilwa Island carbonatite complex were chosen for study. In addition to the main fenite assemblage of feldspar and aegirine ± arfvedsonite, riebeckite and richterite, the fenite contains micro-mineral assemblages including apatite, ilmenite, rutile, magnetite, zircon, rare-earth minerals and pyrochlore in vein networks. Petrography using a scanning electron microscope in energy-dispersive spectroscopy mode showed that the rare-earth minerals (monazite, bastnäsite and parisite) formed later than the fenite feldspar, aegirine and apatite and provide evidence of REE mobility into all grades of fenite. Fenite apatite has a distinct negative Eu anomaly (determined by laser ablation inductively coupled plasma mass spectrometry) that is rare in carbonatite-associated rocks and interpreted as related to pre-crystallization of plagioclase and co-crystallization with K-feldspar in the fenite. The fenite minerals have consistently higher mid REE/light REE ratios (La/Sm ≈ 1.3 monazite, ≈ 1.9 bastnäsite, ≈ 1.2 parisite) than their counterparts in the carbonatites (La/Sm ≈ 2.5 monazite, ≈ 4.2 bastnäsite, ≈ 3.4 parisite). Quartz in the low- and medium-grade fenite hosts fluid inclusions, typically a few micrometres in diameter, secondary and extremely heterogeneous. Single phase, 2- and 3-phase, single solid and multi solid-bearing examples are present, with 2-phase the most abundant. Calcite, nahcolite, burbankite and baryte were found in the inclusions. Decrepitation of inclusions occurred at ∼200°C before homogenization but melting-temperature data indicate that the inclusions contain relatively pure CO2. A minimum salinity of ∼24 wt.% NaCl equivalent was determined. Among the trace elements in whole-rock analyses, enrichment in Ba, Mo, Nb, Pb, Sr, Th and Y and depletion in Co, Hf and V are common to carbonatite and fenite but enrichment in carbonatitic type elements (Ba, Nb, Sr, Th, Yand REE) generally increases towards the inner parts of the aureole. A schematic model contains multiple fluid events, related to first and second boiling of the magma, accompanying intrusion of the carbonatites at Chilwa Island, each contributing to the mineralogy and chemistry of the fenite. The presence of distinct rare-earth mineral microassemblages in fenite at some distance from carbonatite could be developed as an exploration indicator of REE enrichment.

The crystal structure and the chemical composition of uklonskovite from the holotype material was reinvestigated to shed light on its correct chemical formula. On the basis of information gained from this characterization, we revised the formula from NaMg(SO4)OH·2H2O to NaMg(SO4)F·2H2O (F instead of OH). A careful analysis of the structural details together with a critical review of all the chemical data listed in the scientific literature for uklonskovite support our redefinition. We also present Raman data for the mineral for the first time. Our proposal was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (voting proposal 16-J).

Five turquoise samples, belonging to the XVII century historical collection of the Real Museo Mineralogico (University of Naples Federico II), were investigated by a multi-methodological approach based on powder X-ray diffraction, electron microprobe analysis in wavelength-dispersive spectroscopy mode, backscattered electron images from scanning electron microscopy in energy-dispersive spectroscopy mode, laser ablation inductively coupled plasma mass spectrometry, Fourier transform infrared and Raman spectroscopy.

The samples originate from Sinai (Egypt), Santa Fè S. Miguel (New Mexico), Saxony (Germany), Montebras Creuse (France) and Nishapur (Khorassan, Iran) and display different mineralogical compositions and various mineral associations. The study has shown the presence of: (1) four minerals of the turquoise group: turquoise, faustite, chalcosiderite and planerite; (2) other phosphates from different groups: wavellite, crandallite, goyazite, gorceixite, variscite, metavariscite, fluorapatite; and (3) other minerals: voltaite, adularia and quartz.

The present investigation is intended to show the mineralogical and geochemical variability of the samples with particular attention to the mineralogical parageneses, textural analyses and trace-element concentrations.

Magnesio-riebeckite from the dumps of the abandoned mine of Varenche (45°47’22’’ N, 7°29’17’’ E), Saint-Barthélemy, Nus, Aosta Valley (Italy), was studied to provide the complete mineral description (including crystal structure) and insights into the crystal-chemistry of riebeckite. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is A(Na0.09K0.01)Σ=0.10B(Na1.77Ca0.11Mg0.08Mn2+ 0:04)Σ=2.00C(Mg2.93Mn2+0:13Fe2+0:07Zn0.01Ni0.12Fe3+1:25Al0.48Ti0.01)Σ=5.00T(Si7.92Al0.08)Σ=8.00 O22W(OH1.88F0.12)Σ=2.00. Magnesio-riebeckite is biaxial (+), with α = 1.678(2), β = 1.682(2), γ = 1.688(2) and 2V (meas.) = 80.2(1.7)°, 2V (calc.) = 78.7°. The unit-cell parameters are a = 9.6481(14), b = 17.873(3), c = 5.3013(7) Å, β = 103.630(2)°, V = 888.4 (2)Å3, Z = 2, space group C2/m. The strongest ten reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 2.701, 100, (151); 8.303, 83, (110); 3.079, 62, (310); 3.391, 53, (131); 4.467, 50, (040,021); 2.522, 50, (̅202); 2.578, 35, (061); 2.155, 30, (261), 4.855, 30, (̅111), 2.300, 29, (̅351).

Natural samples containing tetrahedrite–tennantite, bournonite–seligmannite and geocronite–jordanite from the Coranda-Hondol ore deposit, Romania, were investigated by Raman spectroscopy to determine its capability to provide estimates of solid solutions in three common and widespread sulfosalt mineral series. Raman measurements were performed on extended solid solution series (Td1 to Td97, Bnn25 to Bnn93 and Gcn24 to Gcn67, apfu). The tetrahedrite–tennantite and bournonite–seligmannite solid solution series show strong correlations between spectroscopic parameters ( position, relative intensity and shape of the Raman bands) and the Sb/(Sb+As) content ratio, while Raman spectra of geocronite–jordanite shows no evolution of Raman bands. In order to simplify the method used to estimate the Sb/(Sb+As) content ratio in tetrahedrite–tennantite and bournonite–seligmannite series, several linear equations of the first-order polynomial fit were obtained. The results are in good agreement with electron microprobe data. Moreover, a computer program was developed as an analytical tool for a fast and accurate determination of Sb/(Sb+As) content ratio by at least one spectroscopic parameter. These results indicate that Raman spectroscopy can provide direct information on the composition and structure of the tetrahedrite–tennantite and bournonite– seligmannite series.

Here we report a nomenclature and classification for the seidozerite-supergroup minerals. The TS (Titanium-Silicate) block is the main structural unit in all seidozerite-supergroup structures; it consists of a central O (O = Octahedral) sheet and two adjacent H (H = Heteropolyhedral) sheets where Si2O7 groups occur in the H sheets. The TS block is characterized by a planar minimal cell based on translation vectors, t1 and t2, the lengths of these vectors are t1 ≈ 5.5 and t2 ≈ 7 Å, and t1 ^ t2 is close to 90°. The forty-five minerals of the sedozerite supergroup are divided into four groups based on the content of Ti and topology and stereochemistry of the TS block: in rinkite, bafertisite, lamprophyllite and murmanite groups, Ti (+ Nb + Zr + Fe3+ +Mg + Mn) = 1, 2, 3 and 4 apfu (atoms per formula unit), respectively. All TS-block structures consist either solely of TS blocks or of two types of block: the TS block and an I (Intermediate) block that comprises atoms between two TS blocks. Usually, the I block consists of alkali and alkaline-earth cations, H2O groups and oxyanions (PO4)3-, (SO4)2- and (CO3)2-.The general formula of the TS block is as follows AP2 BP2 MH2 MO4 (Si2O7)2X4+n, where MH2 and MO4 = cations of the H and O sheets; MH = Ti, Nb, Zr, Y, Mn, Ca + REE, Ca;MO = Ti, Zr, Nb, Fe3+, Fe2+, Mg, Mn, Zn, Ca, Na; AP and BP = cations at the peripheral (P) sites = Na, Ca + REE, Ca, Zn, Ba, Sr, K; X = anions = O, OH, F, H2O; XO4+n=XO4 +XPn , n = 0, 1, 1.5, 2, 4; XP = XPM and XPA = apical anions of MH and AP cations at the periphery of the TS block.

Fluorcaphite [SrCaCa3(PO4)3F] is a rare strontium-calcium member of the apatite supergroup which was previously known only from the Khibiny and Lovozero alkaline complexes. This paper presents evidence of a third fluorcaphite occurrence. It was found in hydrothermally altered Lower Cretaceous teschenite, which forms an intrusive body (probably a sill) in the Lower Cretaceous siliciclastic flysch sediments at Tichá near Frenštát pod Radhoštěm, Silesian Unit, Outer Western Carpathians (Czech Republic). Fluorcaphite occurs as an accessory mineral in hydrothermal veins and in an adjacent alteration zone within the host teschenite. Vein-hosted fluorcaphite forms euhedral crystals and skeletal crusts enclosed in analcime while the teschenite-hosted fluorcaphite forms small overgrowths on older phenocrysts of magmatic apatite. Fluorcaphite from Tichá contains 0.50–1.97 Sr apfu, 2.96–4.49 Ca apfu, 0.59–1.09 F apfu and significantly lower Na (0.01–0.05 apfu) and LREE contents (up to 0.07 apfu). Fluorcaphite formed under hydrothermal conditions after solidification of the host teschenite during post-magmatic hydrothermal activity at temperatures probably between ∼150 and 300°C. The initial 87Sr/86Sr ratio of vein-hosted analcime +fluorcaphite (0.7063) is significantly higher than those of the host teschenite (0.7041). We therefore suggest a mix of strontium sources in the vein analcime+fluorcaphite: (1) from the host teschenite plus (2) from external source(s) including the Lower Cretaceous seawater and/or surrounding sedimentary rocks of the Silesian Unit. These data indicate an open-system fluid regime and the participation of various fluid sources during the alteration event giving rise to fluorcaphite.

Rutile grains occur extensively in host phases of biotite and quartz-feldspar aggregate in high-temperature paragneisses of the Mogok metamorphic belt of Myanmar. They occur as an isolated phase and sometimes show intergrowth texture with ilmenite. Most rutile grains contain up to 3.7 wt.% Nb2O5, which shows positive correlations with Fe and trivalent elements. Niobium substitutes for Ti by a coupled substitution with the trivalent cations (M3+) of Nb5+M3+Ti4+-2. Fine-grained rutile grains included in ilmenite are distinctly poor in Nb (<0.1 wt.% as Nb2O5) and contain Fe of 1.7–3.2 wt.% as Fe2O3, suggesting vacancybearing substitution of Fe3+4 Ti4+-3□–1, where □ indicates a vacancy. The rutile grains in the felsic phases contain high Zr contents of up to 4200 ppm, suggesting equilibrium temperatures over 800°C using the Ti-in-rutile geothermometer. These high-temperature conditions are consistent with those estimated by conventional methods reported in the literature and suggest widespread occurrences of the upperamphibolite and granulite facies metamorphic rocks in the middle segment of the Mogok metamorphic belt. In contrast, the Zr contents of rutile grains in biotite are usually <1000 ppm, implying equilibrium temperatures lower than 750°C. Most of the rutile grains poorer in Zr might have been included in biotite and were isolated from the zircon-bearing system during an early stage of prograde metamorphism. Some other rutile grains poorer in Zr might have been an exsolved phase from Ti-rich biotite during retrograde metamorphism, which was furthered by the infiltration of metamorphic fluid under lower-amphibolite facies conditions.

The new mineral magnesiocanutite (IMA2016-057), NaMnMg2[AsO4]2[AsO2(OH)2], was found at the Torrecillas mine, Iquique Province, Chile, where it occurs as a secondary phase in association with anhydrite, canutite, halite, lavendulan and magnesiokoritnigite. Magnesiocanutite occurs as pale brownish-pink to rose-pink, lozenge-shaped tablets that are often grouped in tightly intergrown aggregates. The crystal forms are {110} and {102}. Crystals are transparent, with vitreous lustre and white to very pale pink streak. The Mohs hardness is 2½, tenacity is brittle, and the fracture is splintery. Crystals exhibit two perfect cleavages: {010} and {101}. The calculated density is 3.957 g/cm3. Optically, magnesiocanutite is biaxial (+), with α = 1.689(2), β = 1.700(2), γ = 1.730(2) (measured in white light); 2Vmeas. = 64.3(4)°; slight dispersion, r <v; orientation Z = b; X ∧ a = 15° in obtuse angle β. The mineral is slowly soluble in dilute HCl at room temperature. Electron-microprobe analyses, provided Na2O 5.44, CaO 0.26, MgO 8.84, MnO 18.45, CoO 1.47, CuO 2.13, As2O5 59.51, H2O(calc) 2.86, total 98.96 wt.%. Magnesiocanutite is monoclinic, C2/c, a = 12.2514(8), b = 12.4980(9), c = 6.8345(5) Å, β = 113.167(8)°, V = 962.10(13) Å3 and Z = 4. The eight strongest powder X-ray diffraction lines are [dobs Å(I )(hkl)]: 6.25(42)(020), 3.566(43)(310,1̄31), 3.262(96)(1̄12), 3.120(59)(002,131,040,221), 2.787(93)(400,022,041,330), 2.718(100) (4̄21,240,112,402), 2.641(42)(1̄32) and 1.5026(43)(multiple). Magnesiocanutite has a protonated alluaudite-type structure (R1 = 2.59% for 789 Fo > 4σF reflections) and is the Mg analogue of canutite. Using the results of both the microprobe analyses and structure refinement, the structurally based empirical formula is Na(Mn0.78Mg0.22)Σ1.00(Mg1.04Mn0.70Cu0.15Co0.11)Σ2.00[AsO4]2[AsO2(OH)2].

The crystal structure and chemical formula of zvyaginite, ideally Na2ZnTiNb2(Si2O7)2O2(OH)2(H2O)4, a lamprophyllite-group mineral of the seidozerite supergroup from the type locality, Mt. Malyi Punkaruaiv, Lovozero alkaline massif, Kola Peninsula, Russia have been revised. The crystal structurewas refined with a new origin in space group C1, a = 10.769(2), b = 14.276(3), c = 12.101(2) Å, α = 105.45(3), β = 95.17(3), γ = 90.04(3)°, V = 1785.3(3.2) Å3, R1 = 9.23%. The electron-microprobe analysis gave the following empirical formula [calculated on 22 (O + F)]: (Na0.75Ca0.09K0.04□1.12)Σ2 (Na1.12Zn0.88Mn0.17Fe2+0.04□0.79)Σ3 (Nb1.68Ti1.25Al0.07)Σ3 (Si4.03O14)O2 [(OH)1.11F0.89]Σ2(H2O)4, Z = 4. Electron-diffraction patterns have prominent streaking along c* and HRTEM images show an intergrowth of crystalline zvyaginite with two distinct phases, both of which are partially amorphous. The crystal structure of zvyaginite is an array of TS (Titanium-Silicate) blocks connected via hydrogen bonds between H2O groups. The TS block consists of HOH sheets (H = heteropolyhedral, O = octahedral) parallel to (001). In the O sheet, the [6]MO(1,4,5) sites are occupied mainly by Ti, Zn and Na and the [6]MO(2,3) sites are occupied by Na at less than 50%. In the H sheet, the [6]MH(1,2) sites are occupied mainly by Nb and the [8]AP(1) and [8]AP(2) sites are occupied mainly by Na and □. The MH and AP polyhedra and Si2O7 groups constitute the H sheet. The ideal structural formula is Na□Nb2NaZn□Ti(Si2O7)2O2(OH)2(H2O)4. Zvyaginite is a Zn-bearing and Na-poor analogue of epistolite, ideally (Na□)Nb2Na3Ti(Si2O7)2O2(OH)2(H2O)4. Epistolite and zvyaginite are related by the following substitution in the O sheet of the TS-block: (Naþ 2 )epi↔Zn2+ zvy +□zvy. The doubling of the t1 and t2 translations of zvyaginite relative to those of epistolite is due to the order of Zn and Na along a (t1) and b (t2) in the O sheet of zvyaginite.

Significant uncertainty surrounds the processes involved in the formation of basalt-hosted corundum, particularly the role that the mantle plays in corundum generation. Some previous studies have suggested that trace-element ratios (namely, Cr/Ga and Ga/Mg) are useful for distinguishing two types of corundum: ‘magmatic’ and ‘metamorphic’, designations that include mantle and crustal processes. However, recent studies, including this one, have discovered transitional groups between these end-members that are difficult to classify.We used laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) to measure trace-element concentrations in sapphire and ruby crystals from eight alluvial deposits that span a significant length of the eastern Australian gemstone belt. Additionally, we collected LA–ICP–MS U–Pb and traceelement data from zircon megacrysts atWeldborough, Tasmania, which is also within the gemstone belt. Our sapphire and ruby results reveal a continuum in trace-element compositions, an observation that raises questions regarding previous classifications that ascribe corundum from basalt-hosted gemfields to either ‘magmatic’ or ‘metamorphic’ sources. The spatial association of basalt-related gemfields in eastern Australia with a long-lived convergent margin suggests a link between corundum formation and Al-enrichment of the mantle wedge during periods of subduction.