A comparison of Rietveld refinement results for a bauxite-bearing regolith and its clayey cover in the Amazon region was made with stoichiometric calculations from chemical analysis and partly from thermogravimetric results. For this investigation a profile in the bauxite-bearing regolith occurrence in the ALCOA bauxite mine at Juruti, Brazil was studied. The different minerals, their compositions and their low crystallinity in the different horizons were investigated and the contents determined. It is evident that some minerals show several generations and some chemical composition changes that must be included in the Rietveld refinement. Al-rich hematites and goethites are common along the bauxite profile. Amorphous contents were determined with rutile added as an internal standard and shown to have gibbsite- or kaolinite-like composition. The minerals could be quantified in the different horizons and the difficulties were mainly related to variable crystalline aspects of the phases. Rietveld refinement can be a powerful tool in bauxite prospecting, quality control and during mining and beneficiation of ore minerals using the adapted refinement strategies.

A study of the cathodoluminescence (CL) properties of imperial topaz from Ouro Preto region (Minas Gerais state, Brazil) and its relation with trace-element composition was conducted, using scanning electron microscope cathodoluminescence (SEM-CL), optical microscope cathodoluminescence (OM-CL), cathodoluminescence-spectrometry (CL-spectrometry), electron microprobe analysis (EMPA), laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) and Raman spectrometry. Each analytical technique allowed characterization of the imperial topaz fingerprint. SEM-CL panchromatic images show different crystal growth and resorption events in imperial topaz crystals. Colour CL images indicate only blue to violet emissions. The CL-spectra indicate a broad emission band with low intensity peak at ~417 nm and a broad emission band with high intensity and major peaks at 685, 698, 711 and 733 nm. The EMPA indicates high OH content, in which the OH/(OH + F) ratio ranges between 0.35–0.43 (0.72 ≤ OH ≤ 0.86 apfu). High Cu and Zn concentrations (LA-ICP-MS) were measured in the high luminescence areas of SEM-CL images, suggesting both elements as CL-activators in imperial topaz. Raman and CL-spectra indicate high Cr concentrations, corroborated by EMPA and LA-ICP-MS results. The high Cr caused strong luminescence intensities that enabled their superimposition over the OH stretching mode (~3650 cm–1) of topaz in all Raman spectra. Among trace elements, the concentrations of Ti, V, Cr, Mn, Fe, Cu, Zn, Ga and Ge provide the fingerprint of imperial topaz.

The quartz-monzonitic intrusion of ‘Botro ai Marmi’ in Tuscany, Italy, can be considered to be a typical example of an intrusion-centred magmatic hydrothermal system. The evolution of hydrothermal fluids in the ‘Botro ai Marmi’ intrusion was investigated using fluid-inclusion analyses to provide suitable physico-chemical constraints on the fluids involved in the late- to post-magmatic hydrothermal activity that affected the intrusion, providing inferences on their origin and variations of temperature and pressure with time.

This work demonstrates that the earliest fluids circulating in the ‘Botro ai Marmi’ intrusion were high-temperature brines exsolved directly from the crystallizing magma. This fluid circulated in the intrusion under lithostatic conditions (P > 90 MPa, T > 540°C). A second evolutionary stage of the magmatic hydrothermal system is marked by the transition from lithostatic (>90 MPa) to hydrostatic dominated conditions (50 to 10 MPa). In this stage the fluids are also interpreted to be mainly orthomagmatic in origin but unmixed in a high-salinity brine and in a low-salinity vapour aqueous phase, at a temperature ranging from ~500 to 300°C. These fluids were responsible for the potassic alteration facies. At a later stage of hydrothermal evolution, abundant meteoric dominated fluids entered the system and are associated with propylitic alteration. This event marks the transition from a magmatic-hydrothermal system to a typical hydrothermal (‘geothermal’) system, which can be assumed to be similar to some extent to the nearby active high-enthalpy geothermal system of Larderello. Low-temperature and low-salinity meteoric water-dominated fluids characterize the latest stage of the ‘Botro ai Marmi’ hydrothermal system.

Ba-rich and Si-rich phlogopites occur in the talc-bearing rocks of the La Creuse sulfide ore deposit in Beaujolais, France. They form a group of compositions completely separated from the common Al-rich phlogopites that occur in the surrounding talc-free metasiltites and metarhyolites, with higher Ba and Mg and lower Al contents. The Ba-rich phlogopites have a relatively narrow compositional range (0.24 to 0.80 Ba per formula unit, for 44 valencies) with high and constant Si (5.8 atoms per formula unit, apfu) and Mg + Fe (5.6 apfu), probably buffered by the presence of talc. Compared to low-Al phlogopites from talc-free rocks, the excess charge introduced by the BaK–1 substitution is compensated by interlayer vacancies. Such a high level of interlayer vacancy (0.56 pfu), related to the talc-producing metasomatic conditions, is essential for the stability of this special group of Ba-rich and Si-rich phlogopites.

Single crystal X-ray diffraction analyses were performed. Ba-rich and Si-rich phlogopite is monoclinic, space group C2/m, (R = 5.31%) with a = 5.3185(5), b = 9.2136(9), c = 10.1349(11) Å and β = 100.131(11)°. The occupancies of Mg/Fe and K/Ba were refined exploring different vacancies. The solutions giving the best R factor (4.77%) and goodness-of-fit (1.06) are obtained with 15% < vacancy < 40% at the interlayer site.

The crystal structure of ceruleite, CuAl4[AsO4]2(OH)8(H2O)4, has been solved to an R1 of 0.0307, using the world's largest crystals from the Cap Garonne mine, France. Ceruleite crystallizes in space group P21/n, with the unit cell a = 7.2000(14), b = 11.345(2), c = 9.856(2) Å, β = 105.57(3)°, V = 775.6(3) Å3 and Z = 1. Ceruleite has a unique structure that consists of Al(O,OH)6 octahedra that are sharing edges to form rhombus-shaped tetramers. AsO4 tetrahedra share two corners with one such rhombus and the other two corners with each of two other rhombi, linking them into a very open mesoporous framework. Cu(OH)2(H2O)2 squares lie in the channels and link Al4 rhombi along || b. H2O molecules are also located in the channels.

Millsite, CuTeO3·2H2O, is a new mineral from Gråurdfjellet in Oppdal, Norway. It occurs as a minor secondary phase alongside teineite, other copper secondaries and relict primary tellurides in a boulder of quartz-rich granite, which is probably a glacial erratic. Millsite is bright cyan to royal blue in colour. The mineral is transparent to slightly translucent with a vitreous lustre and has a perfect (100) cleavage. It is brittle, has a conchoidal fracture and a pale green streak. Millsite is optically biaxial (+), α = 1.756(5), β = 1.794(5), γ = 1.925calc and 2Vmeas = 60(1)°. Millsite has monoclinic space group P21/c, with a = 7.4049(2) Å, b = 7.7873(2) Å, c = 8.5217(2) Å, β = 110.203(3)°, V = 461.17(2) Å3 and Z = 4. The empirical formula is Cu0.99(Te0.98Se0.02)O3(H2O)2. The five strongest reflections in the powder X-ray diffraction pattern are [dhkl in Å (hkl, Irel%)]: 6.954 (100, 100), 3.558 (012, 64), 2.838 (12$\bar 2$, 47), 2.675 (211, 43) and 3.175 (210, 39). The crystal structure has been determined to R1 = 0.016, wR2 = 0.036 and GooF = 1.049. The diagnostic structural unit of millsite consists of a Cu2O6(H2O)4 dimer that is decorated with four TeO3 groups connecting adjacent dimers and defining (100) heteropolyhedral sheets. These heteropolyhedral sheets are only connected by layers of structurally significant hydrogen bonds and correlate with the (100) cleavage. Millsite is a polymorph of teineite with a unique configuration of the M2O6(H2O)4 dimer that leads to a sheet topology. No isostructural selenium or tellurium analogue exists. The monoclinic polymorph (P21/c) of chalcomenite ‘monoclinic-CuSeO3·2H2O’ hereafter, ahlfeldite and MgSeO3·2H2O have M2O6(H2O)4 dimers, but their configuration differs significantly from that of millsite and leads to a framework topology rather than a sheet. Teineite does not have a dimeric structure and so is fundamentally different from millsite. The sheet topology of millsite appears to be unique among tellurites.

A genetic linkage between W, (Cu, Mo)-mineralization and chlorite minerals, and the discrimination of different mineralization events in the magmatic-hydrothermal system of Borralha, northern Portugal, is discussed on the basis of textural relationships, crystal chemistry and stable isotopic data obtained from chlorite. Chlorite minerals were identified in assemblages with quartz, feldspars, tungstates and sulfides. X-ray diffraction studies of selected chlorite minerals shows a trioctahedral structural type. Electron probe micro-analyses identified four different compositions and associations: (1) Fe,Mn-chlorite with scheelite I; (2) Fe-chlorite with wolframite + scheelite II ± sulfide; (3) Fe,Mg-chlorite with molybdenite + bismuthinite; and (4) Mg,Fe-chlorite with chalcopyrite. The composition of Fe-chlorite (Al3.01Fe3+0.25Fe2+7.95Mn0.26Mg0.19)11.66(Si5.44Al2.56)8O20(OH)8 corresponds to daphnite and Fe,Mn-chlorite (Al2.69Fe3+0.02 Fe2+7.54Mn1.08Mg0.62)11.89(Si5.31Al2.68)4O20(OH)8 to a mixed composition between daphnite and amesite. The Fe,Mg-chlorite (Al2.89Fe3+0.24Fe2+6.42Mn0.21Mg2.08)11.84 (Si5.31Al2.79)8F0.31O20(OH)8 corresponds to ripidolite and Mg,Fe-chlorite (Al2.63Fe3+0.37Fe2+1.72Mn0.01Mg6.40Ca0.26)11.39(Si6.02Al1.98)8O20(OH)8 to pychnochlorite.

Chlorite geothermometry estimates a temperature for Fe,Mn-chlorite (scheelite I) from 400°C to 500°C, for Fe-chlorite (Mn-rich wolframite + scheelite II ± sulfide) from 250 to 350°C, for Fe,Mg-chlorite (Mo-mineralization) from 200°C to 250°C and for Mg,Fe-chlorite at ~150°C. Oxygen isotopes (V-SMOW) yielded values of +3.8 (1σ) (Fe-chlorite), +6.91 (1σ) (Fe,Mn-chlorite) and +1.5 (1σ) (Fe,Mg-chlorite). The calculated δ18OF of Fe- and Fe,Mg-chlorite is ~+3.75 (1σ) and +1.45 (1σ) for the mineralizing fluid, whereas for Fe,Mn-chlorite it is +8.17 (1σ). The δ18O data obtained from quartz in W- and Mo-mineralization yielded values of +12.6 and +11.4 (1σ), whereas for adularia δ18O is about +10 (1σ). These estimates allow us to conclude that the Fe,Mn-chlorite crystallized from a magmatic-hydrothermal fluid, whereas the Fe- and Fe,Mg-chlorite quartz and adularia resulted from a mixed contribution between meteoric and magmatic-hydrothermal fluid.

The Troodos ophiolite Cyprus hosts the type locality for Cyprus-type, mafic volcanogenic massive sulfide (VMS) deposits. Regional soil geochemical data for Troodos are highly variable with the Solea graben, one of three regional graben structures on Cyprus, showing enrichment in Te and Se. Of the three VMS sampled within the Solea graben, Apliki exhibits the most significant enrichment in Se. Samples from the South Apliki Breccia Zone; a zone of hematite-rich breccia containing euhedral pyrite and chalcopyrite, contain up to 4953 and 3956 ppm Se in pyrite and chalcopyrite, respectively. Four paragenetic stages are identified at Apliki and different generations of pyrite are distinguishable using trace-element chemistry analysed via laser ablation inductively coupled plasma mass spectrometry. Results indicate stage I pyrite formed under reduced conditions at high temperatures >280°C and contains 182 ppm (n = 22 σ = 253) Se. Late stage III pyrite which is euhedral and overprints chalcopyrite and hematite is enriched in Se (averaging 1862 ppm; n = 23 σ = 1394). Sulfide dissolution and hematite formation displaced large amounts of Se as hematite cannot accommodate high concentrations of Se in its crystal structure. The mechanisms proposed to explain the pronounced change in redox are twofold. Fault movement leading to localized seawater ingress coupled with a decreasing magmatic flux that generated locally oxidizing conditions and promoted sulfide dissolution. A Se/S ratio of 9280 indicates a probable magmatic component for late stage III pyrite, which is suggested as a mechanism explaining the transition from oxidizing back to reduced conditions. This study highlights the significance of changes in redox which promote sulfide dissolution, mobilization and enrichment of Se.

The present work deals with the synthesis of kalsilite using material from a kaolinitic rock outcrop in Romana, Sassary Province, Sardinia, Italy.

The hydrothermal synthesis method required the dissolution of kaolin and Al(OH)3 in a KOH solution at a temperature of 190°C and 1.013 bar. Crystallization of kalsilite was confirmed at 12 h in association with kaliophilite H2 as a metastable phase.

The products of synthesis were fully characterized by powder X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, infrared spectroscopy and 29Si nuclear magnetic resonance. The amorphous phase in the synthesis powders was estimated with quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. Cell parameters and density were also calculated for the kalsilite. A potential application of kalsilite was investigated as a heterogeneous catalyst for biodiesel synthesis from sunflower oil used for frying.

The spinel-group minerals, found in a range of igneous rocks, are resistant to weathering and can incorporate several multivalent elements, meaning they have the potential to provide insight into the redox conditions of parental magmas. Naturally occurring spinel can contain varying quantities of Mn, an element which occurs terrestrially and extra-terrestrially as Mn2+, Mn3+, Mn4+ and Mn5+. However, a lack of information on the effects of oxygen fugacity ($f_{{\rm O}_{\rm 2}}$) on: (1) Mn valence state and cation distribution; and (2) on spinel-melt partitioning means that the potential for a Mn-in-spinel oxy-barometer remains largely untested. Here, we use electron probe microanalysis, micro-focus X-ray Absorption Near Edge Structure (XANES) spectroscopy and single-crystal X-ray diffraction (SC-XRD) to investigate cation distribution and valence state in spinels in the Al–Mn–O and Fe–Mn–O systems synthesized at ambient pressure under varying $\hskip 2pt f_{{\rm O}_{\rm 2}}$ conditions. In contrast to previous studies, we find that the spectral resolution of the Mn K-edge XANES spectra is insufficient to provide quantitative data on Mn valence state and site occupancy, although it does verify that Mn is incorporated as both Mn2+ and Mn3+, distributed over tetrahedral and octahedral sites. Combination of data from XANES and SC-XRD refinements can, however, be used to model Mn, Al and Fe valence and site occupancy. It would be expected that Mn–Fe spinels have the potential to record $f_{{\rm O}_{\rm 2}}$ conditions in parental melts due to changes to the octahedral site under conditions that were more reducing. However, decoupling the effects of temperature and oxygen fugacity on the TFe3+–TMn2+ exchange in the Mn–Fe spinels remains challenging. In contrast, little variation is noted in Mn–Al spinels as a function of $\hskip 2pt f_{{\rm O}_{\rm 2}}$, implying that crystal chemistry and cation site geometry may significantly influence cation distribution, and by inference, crystal-melt partitioning, in spinel-group minerals.

Mineralogical, electron microprobe analysis and laser ablation-inductively coupled plasma-mass spectrometry data from molybdenite within two porphyry copper deposits (Kalinovskoe and Birgilda) of the Birgilda-Tomino ore cluster (South Urals) are presented.† The results provide evidence that molybdenites from these two sites have similar trace-element chemistry. Most trace elements (Si, Fe, Co, Cu, Zn, Ag, Sb, Te, Pb, Bi, Au, As and Se) form mineral inclusions within molybdenite. The Re contents in molybdenite vary from 8.7 ppm to 1.13 wt.%. The Re distribution within single molybdenite flakes is always extremely heterogeneous. It is argued that a temperature decrease favours the formation of Re-rich molybdenite. The high Re content of molybdenite observed points to a mantle-derived source.

Clino-suenoite, ideally □${\rm Mn}_{2}^{2 +} $Mg5Si8O22(OH)2 is a new amphibole of the magnesium-iron-manganese subgroup of the amphibole supergroup. The type specimen was found at the Lower Scerscen Glacier, Valmalenco, Sondrio, Italy, where it occurs in Mn-rich quartzite erratics containing braunite, rhodonite, spessartine, carbonates and various accessory minerals. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: ANa0.04B(${\rm Mn}_{1.58}^{2 +} $Ca0.26Na0.16)Σ2.00C(Mg4.21${\rm Mn}_{0. 61}^{2 +} {\rm Fe}_{0.04}^{2 +} $Zn0.01Ni0.01${\rm Fe}_{0.08}^{3 +} $Al0.04)Σ5.00TSi8.00O22W[(OH1.94F0.06)]Σ=2.00. Clino-suenoite is biaxial (+), with α = 1.632(2), β = 1.644(2), γ = 1.664(2) and 2Vmeas. = 78(2)° and 2Vcalc. = 76.3°. The unit-cell parameters in the C2/m space group are a = 9.6128(11), b = 18.073(2), c = 5.3073(6) Å, β = 102.825(2)° and V = 899.1(2) Å3 with Z = 2. The strongest ten reflections in the powder X-ray diffraction pattern [d (in Å), I, (hkl)] are: 2.728, 100, (151); 2.513, 77, ($\bar 2$02); 3.079, 62, (310); 8.321, 60, (110); 3.421, 54, (131); 2.603, 42, (061); 2.175, 42, (261); 3.253, 41, (240); 2.969, 40, (221); 9.036, 40, (020).

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.

The Waterberg platinum deposit is an extraordinary example of a vein-type hydrothermal quartz-hematite-PGE (platinum-group element) mineralization. This study concentrates on the geochemical character of the ores and the platinum-group mineral (PGM) assemblage by application of reflected-light and scanning electron microscopy followed by electron probe microanalysis.

The PGM-bearing quartz veins show multiple banding indicating numerous pulses of fluid infiltration. Mineralization was introduced contemporaneously with the earliest generation of vein quartz and hematite. High oxygen and low sulfur fugacities of the mineralizing fluids are indicated by hematite as the predominant opaque mineral and the lack of sulfides.

The ‘Waterberg type’ mineralization is characterized by unique metal proportions, namely Pt>Pd>Au, interpreted as a fingerprint to the cradle of the metals, namely rocks and ores of the Bushveld Complex, or reflecting metal fractionation during ascent of an oxidized, evolving fluid. The PGM assemblage signifies three main depositional and alteration events. (1) Deposition of native Pt and Pt–Pd alloys (>90% of the PGM assemblage) and Pd–Sb–As compounds (Pt-rich isomertieite and mertieite II) from hydrothermal fluids. (2) Hydrothermal alteration of Pt by Cu-rich fluids and formation of Pt–Cu alloys and hongshiite [PtCu]. (3) Weathering/oxidation of the ores producing Pd/Pt-oxides/hydroxides.

Platinum-group element transport was probably by chloride complexes in moderately acidic and strongly oxidizing fluids of relatively low salinity, and depositional temperatures were in the range 400–200°C. Alternatively, quartz and ore textures may hint to noble metal transport in a colloidal form and deposition as gels.

The source of the PGE is probably in platiniferous rocks or ores of the Bushveld Complex which were leached by hydrothermal solutions. If so, further Waterberg-type deposits may be present, and a prime target area would be along the corridor of the Thabazimbi-Murchison-Lineament where geothermal springs are presently still active.