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In the Lesina Marina village area, the cropping out gypsum rocks, that rose up from the deep and thick Upper Trias Burano Fm anhydrite layer, have been analyzed to investigate the trigger mechanism for their ascent. In this regard, we focus on the anhydrite-to-gypsum transformation starting from the deep source layer. Indeed, petrographic observations of the widespread corroded anhydrite crystals embedded in these gypsum rocks revealed unequivocal evidences of the anhydrite-to-gypsum transformation. In addition, and referring to gypsum, microstructural features indicate that ductile deformation mechanisms initially operated under higher temperature conditions. This temperature should be close to 107 °C, namely the value of the upper temperature limit of stability of gypsum from Lesina Marina, above which it starts to transform and dehydrate, as revealed by microthermometry heating/dehydration experiments combined with micro-Raman analyses. All these evidences are in favor of the dramatic density decrease and volume increase due to anhydrite-to-gypsum transformation by hydration in the deep source layer; these variations of physical conditions, triggered by hydration, promoted diapirism of the gypsum mass, in other words “hydration diapirism”. As revealed by seismic lines interpretation, the diapirism, which gave rise to the Lesina diapir, occurred during Plio-Pleistocene and was genetically related to the Lesina graben-type structure. Hydration at depth was favored by the downward circulation of water-rich fluids channeled in faults, and the gypsum mass used the weakened zone of the southern fault to pierce the overlying Mesozoic and Tertiary sediments.

The thermal behavior of melanterite from the Fornovolasco mine (Tuscany, Italy) has been investigated via differential thermal analysis (DTA), thermogravimetry (TG), in situ high-temperature X-ray powder diffraction (XRPD) and Fourier-transform infrared spectroscopy (FTIR). The DTA curve showed endothermic peaks at 70, 100, 260, 500–560 and 660 °C whereas the TG curve evidenced a total mass decrease of ~68%, in keeping with the loss of all H2O and SO4 groups. Rietveld refinements were performed for all the collected patterns in the 25–775 °C range and converged at 1.57 ≤ R (%) ≤ 2.75 and 1.98 ≤ Rwp (%) ≤ 3.74. The decomposition steps FeSO4·7H2O → FeSO4·4H2O (25 ≤ T ≤ 50 °C) → FeSO4·H2O (50 &lt, T ≤ 100 °C) → FeOHSO4 (75 &lt, T ≤ 200 °C) → Fe2(SO4)3 (400 &lt, T ≤ 500 °C) → Fe2O3 (500 &lt, T ≤ 775 °C) were obtained. The high-temperature infrared analysis confirmed that melanterite undergoes a three-step dehydration in the 25–300 °C temperature range. The FeOHSO4 phase is stable over a wide range of temperature and transforms partially to Fe2(SO4)3 without the formation of Fe2O(SO4)2. The findings highlight a different behavior of the studied sample with respect to the synthetic salt.

A multi-methodical characterization of a sauconite (Zn-bearing trioctahedral smectite) specimen from the Skorpion ore deposit (Namibia) was performed by combining X‑ray powder diffraction (XRPD), cation exchange capacity (CEC) analysis, differential thermal analysis (DTA), thermo‑ gravimetry (TG), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM‑HRTEM‑AEM). The X‑ray diffraction pattern exhibits the typical features of turbostratic stacking disorder with symmetrical basal 00l reflections and long‑tailed hk bands, as confirmed by TEM observations. Besides sauconite, the sample contains minor amounts of kaolinite, dioctahedral smectite, and quartz. CEC analysis provides a total of Ca (~69%), Mg (~26%), Na (~4%), and K (0.7%) exchangeable cations. Therefore, Zn is located exclusively within the octahedral site of sauconite. TG analysis of the sample yields a total mass loss of about 17%. Three endothermic peaks can be observed in the DTA curve, associated with dehydration and dehydroxylation of the material. An exothermic peak at 820 °C is also present as a consequence of decomposition and recrystallization. The infrared spectrum shows the typical ZnOH stretching signature at 3648 cm, whereas, in the OH/HO stretching region two bands at 3585 and 3440 cm can be attributed to stretching vibrations of the inner hydration sphere of the interlayer cations and to absorbed HO stretching vibration, respectively. Diagnostic bands of kaolinite impurity at ~3698 and 3620 cm are also found, whereas 2:1 dioctahedral layer silicates may contribute to the 3585 and 3620 cm bands. Finally, using the one-layer supercell approach implemented in the BGMN software, a satisfactory XRPD profile fitting model for the Skorpion sauconite was obtained. These findings have implications not only for economic geology/recovery of critical metals but also, more generally, in the field of environmental sciences., The XRPD laboratory at the Dipartimento di Scienze della Terra and Geoambientali, University of Bari “Aldo Moro”, was funded by Potenziamento Strutturale PONa3_00369 “Laboratorio per lo Sviluppo Integrato delle Scienze e delle TEcnologie dei Materiali Avanzati e per dispositivi innovativi (SISTEMA)”. The XRPD facility at the DiSTAR, University “Federico II” Napoli, is acknowledged. The authors acknowledge Annett Steudel and Katja Emmerich for CEC measurement at the Competence Center for Material Moisture, University of Karlshrue, Germany. GB and NM thank Maria Boni, invaluable scientific guide who promoted the study of the economic geology of worldwide nonsulfide ore deposits, and G. Arfè who firstly characterized the Skorpion samples and for continuous help and fruitful discussions. This work was partly supported by DiSTAR fund 2017 (University of Naples Federico II, Italy) granted to G. Balassone, as well as by the research projects PGC2018-094573-B-100 from the Spanish Government and the Research Group RNM-179 of the Junta de Andalucía granted to F. Nieto. Two anonymous referees are thanked for insightful comments that helped to improve the quality of the manuscript.

We report in this paper a new crystal-chemical study of synthetic basic ferric sulfate FeOHSO4. The structure solution performed by the Endeavour program, from new X-ray powder diffraction (XRPD) data, indicated that the correct space group of the monoclinic polytype of FeOHSO4 is C2/c. Selected Area Electron Diffraction (SAED) patterns are also consistent with this structure solution. The arrangement of Fe and S atoms, based on linear chains of Fe3+ octahedra cross-linked by SO4 tetrahedra, corresponds to that of the order/disorder (OD) family. The positions of the hydrogen atoms were located based on DFT calculations. IR and Raman spectra are presented and discussed according to this new structure model. The decomposition of FeOHSO4 during heating was further investigated by means of variable temperature XRPD, thermogravimetry, and differential thermal analysis as well as IR and Raman spectroscopies.

This study is focused on a barian titanian phlogopite found in an alkaline ultramafic dyke transecting Mesozoic limestones of the Gargano Promontory (Apulia, Italy). The rock containing the barian titanian phlogopite, an olivine-clinopyroxene-rich lamprophyre with nepheline and free of feldspars, has been classified as monchiquite. The present study combines chemical analyses, single crystal X-ray diffraction and Raman spectroscopy. Chemical variations suggest that the entry of Ba into the phlogopite structure can be explained by the exchange Ba + Al = K + Si. The crystal structure refinement indicates that the Ti uptake is consistent with the Ti–oxy exchange mechanism. The structural parameters associated with the oxy substitution mechanism are extremely enhanced and rarely reported in natural phlogopite: (a) displacement of M2 cation toward the O4 site (~0.7), (b) M2 octahedron bond-length distortion (~2.5), (c) very short c cell parameter (~10.14 Å). Raman analysis showed most prominent features in the 800–200 cm−1 region with the strongest peaks occurring at 773 and 735 cm−1. Only a weak, broad band was observed to occur in the OH-stretching region. As concerns the origin of the barian titanian phlogopite, the rock textural features clearly indicate that it crystallized from pockets of the interstitial melt. Here, Ba and Ti enrichment took place after major crystallization of olivine under fast-cooling conditions, close to the dyke margin.

The crystal structure of ferrinatrite, Na3[Fe(SO4)3]·3H2O, was refined based on a new single-crystal X-ray diffraction experiment on a sample from the type locality Sierra Gorda, Chile. The data allowed H to be successfully located and the H-bonding system to be defined. Infrared and Raman spectra are presented and discussed for this compound on the basis of the crystal structure. The Oacceptor···H–Odonor bond distances determined from the structure refinement agree well with the geometric correlation obtained from spectroscopic data. The thermal stability and dehydration process of ferrinatrite was investigated by in situ high temperature (HT) synchrotron X-ray powder diffraction, Raman and Fourier transform infrared spectroscopies.

The garnierite ore at Campello Monti occurs as dark green colloform concretions covering surfaces, fractures, and filling veins in harzburgite rocks. The representative composition (Ni2.45Mg0.14Cu0.12Co0.05)Σ2.76Si2.10O5(OH)4 is consistent with a 7 Å phase, namely pecoraite or népouite. Relevant chemical features are an exceptionally high Ni/Mg ratio, a significant level of Cu substituting for Ni, and a low content of S, possibly in tetrahedral sites. Olivine and orthopyroxene in the harzburgite host rock are only partially serpentinized, do not contain detectable Ni, and are almost iron free. The green coating probably originated from groundwater solutions that leached nearby weathered peridotites and sulfide ores, and deposited less-mobile elements along fractures and voids of the host peridotite, just outside their provenance area. Bulk techniques such as X-ray powder diffraction and infrared spectroscopy do not confidently distinguish between népouite and pecoraite, although the comparison with synthetic, implicitly pure polymorphs indicates népouite as the best matching phase. On the other hand, HRTEM clearly shows that garnierite is mostly constituted by plumose aggregates made of curved crystals with frayed tips, a few nanometers thick along the stacks and a few tens of nanometers long (nanoflakes). All known lizardite stacking sequences, namely 1T, 2H1, and 2H2, have been locally observed, even though most crystals show stacking disorder. The recorded nanostructure suggests possible explanations for the recurrent anomalies (low oxide totals, high IVT/VIM cation ratios, etc.) found in EMP analyses of garnierites. The small grain size, the high density of defects, and the structural arrangement actually intermediate between lizardite and chrysotile probably explain the ambiguities that occurred during the characterization with bulk techniques. The results obtained in this study may have important implications for ore processing methods

Fluorine-, boron- and magnesium-rich metamorphosed xenoliths occur in the Campanian Ignimbrite deposits at Fiano (southern Italy), at ∼50 km northeast of the sourced volcanic area. These rocks originated from Mesozoic limestones of the Campanian Apennines, embedded in a fluid flow. The Fiano xenoliths studied consist of ten fluorophlogopite-bearing calc-silicate rocks and five carbonate xenoliths, characterized by combining mineralogical analyses with whole-rock and stable isotope data. The micaceous xenoliths are composed of abundant idiomorphic fluorophlogopite, widespread fluorite, F-rich chondrodite, fluoborite, diopside, Fe(Mg)-oxides, calcite, humite, K-bearing fluoro-richterite and grossular. Of the five mica-free xenoliths, two are calcite marbles, containing subordinate fluorite and hematite, and three are weakly metamorphosed carbonates, composed only of calcite. The crystal structure and composition of fluorophlogopite approach that of the end-member. The Fiano xenoliths are enriched in trace elements with respect to the primary limestones. Comparisons between the rare-earth element (REE) patterns of the Fiano xenoliths and those of both Campanian Ignimbrite and Somma-Vesuvius marble and carbonate xenoliths showthat the Fiano pattern overlaps that of Somma-Vesuvius marble and carbonate xenoliths, and reproduces the trend of Campanian Ignimbrite rocks. Values of δ13C and δ18O depict the same trend of depletion in the heavy isotopes observed in the Somma-Vesuvius nodules, and is related to thermometamorphism. Trace-element distribution, paragenesis, stable isotope geochemistry and data modelling point to infiltration of steam enriched in F, B,Mg and As into carbonate rocks at a temperature of ∼300–450°C during the emplacement of the Campanian Ignimbrite.

A multi-proxy record based on calcareous plankton, dinocysts, pollen, mineralogy and grain size has been acquired from the “Ideale” section, the portion of Montalbano Jonico succession (Southern Italy) that could host the GSSP for the Middle Pleistocene. The direct correlation between marine and terrestrial proxies provides a valuable indication of atmospheric and oceanic connections. The record shows a distinct climate variability well expressed by the vegetational changes, sediment input into the basin and sea surface–water modifications. Biotic proxies indicate that, during the study interval, periods of prevailing subpolar/transitional surface–water conditions were concurrent with steppe and halophytic vegetation. Erosional processes on the hillslopes and terrigenous supply, during these periods, were likely favored due to reduced arboreal vegetation, as attested to by sediment composition and pollen assemblages. Temperate/subtropical surface water conditions were concomitant with prevalent expansions of thermophilous arboreal plants and moister conditions on land, which likely promoted chemical weathering leading to an enhanced supply of kaolinite and smectite in the basin. A relationship between mineral content and the nature of the outcropping units in the source area, as well as sea-level fluctuations, has also been considered. A well-defined period of polar–subpolar water incursion, ranging from 793.2 ka to 788.1 ka, matches the major expansion of steppic vegetation on land and the increase of terrigenous supply into the basin. It likely represents the local response to North Atlantic ice-rafted debris deposition. Short-lived warming/cooling episodes punctuate the latest part of MIS 20 and are tentatively correlated with analogue climate phases predating MIS 1 inception. Full interglacial conditions of MIS 19c, lasting 10.6 kyr, started at 784.3 ka and were characterized by warm, oligotrophic and stratified surface–waters coupled with forest expansion, suggesting prevalent warm and humid conditions on land. A potential sapropel-like interval is identified within MIS 19c and correlated to i-cycle 74. The MIS 19c/19b transition is marked, at 773.2 ka, by the reestablishment of millennial-scale variability, similarly to North Atlantic marine and ice-core records. The results improve the paleoclimate framework of a Middle Pleistocene reference section and add further insight regarding climate development across MIS 19 and on potential similarities with its closest Holocene analogue.

The crystal structure of fibroferrite, Fe(OH)SO 4 ·5H 2 O, was studied by means of single-crystal X-ray diffraction and vibrational (FTIR and Raman) spectroscopies. The new diffraction data allowed to successfully locate eleven H positions and to completely define the H bond system that ensures the cohesion of the Fe-O-S chains in the fibroferrite structure. Infrared and Raman spectra are presented for the first time for this compound and commented on the basis of the crystal structure and literature data for sulfate minerals. Both FTIR and Raman spectra show, in the fundamental water stretching region, a very broad absorption extending from 3600 to 2600 cm −1 ; peaks at 3522, 3411 and 3140 cm −1 can be resolved in the Raman pattern. The bands present in the low-wavenumber ( −1 ) region are assigned on the basis of the literature data for similar substances, and the observed multiplicity is in agreement with a symmetry reduction of the sulfate ion in the structure of fibroferrite.

The crystal structure of hohmannite, Fe3+2[O(SO4)2]·8H2O, was studied by means of single-crystal X-ray diffraction (XRD) and vibrational spectroscopy. The previous structural model was confirmed, though new diffraction data allowed the hydrogen-bond system to be described in greater and more accurate detail. Ab initio calculations were performed in order to determine accurate H positions and to support the experimental model obtained from XRD data. Infrared and Raman spectra are presented for the first time for this compound and comments are made on the basis of the crystal structure and the known literature for sulfate minerals.

The thermal dehydration process of fibroferrite, FeOH(SO4)·5H2O, a secondary iron-bearing hydrous sulfate, was investigated by in situ high-temperature synchrotron X-ray powder diffraction (HT-XRPD), in situ high-temperature Fourier transform infrared spectroscopy (HT-FTIR) and thermal analysis (TGA-DTA) combined with evolved gas mass spectrometry. The data analysis allowed the determination of the stability fields and the reaction paths for this mineral as well as characterization of its high-temperature products. Five main endothermic peaks are observed in the DTA curve collected from room T up to 800 °C. Mass spectrometry of gases evolved during thermogravimetric analysis confirms that the first four mass loss steps are due to water emission, while the fifth is due to a dehydroxylation process; the final step is due to the decomposition of the remaining sulfate ion. The temperature behavior of the different phases occurring during the heating process was analyzed, and the induced structural changes are discussed. In particular, the crystal structure of a new phase, FeOH(SO4)·4H2O, appearing at about 80 °C due to release of one interstitial H2O molecule, was solved by ab initio real-space and reciprocal-space methods. This study contributes to further understanding of the dehydration mechanism and thermal stability of secondary sulfate minerals.

A crystal-chemical investigation of vauxite, ideally FeAl 2 (PO 4 ) 2 (OH) 2 ·6H 2 O, from Llallagua (Bolivia) has been performed using a multi-methodological approach based on WDS-electron microprobe, single-crystal X-ray diffraction, and vibrational spectroscopies (Raman and FTIR). The structure was refined in the triclinic P space group, with the following unit-cell constants: a 9.1276(2), b 11.5836(3), c 6.15960(10) A, α 98.3152(10)°, β 92.0139(10)°, γ 108.1695(9)°, and V 610.05(2) A 3 . The vauxite structure is based on a building unit oriented parallel to the c axis and composed of a chain of Fe2 and Al2 edge-sharing octahedra and two chains of corner-sharing P2 tetrahedra and Al1 octahedra, interconnected via corners and P1 tetrahedra. Neighboring building units are interconnected by Al3 octahedra and via Fe1 octahedra. The framework is completed with two non-coordinated water molecules. The latter, together with the two hydroxyl groups and the other four coordinated water molecules, form a complex hydrogen bonding network whose interactions further compact the whole framework. Both FTIR and Raman spectra show, in the H 2 O stretching region, a broad absorption consisting of several overlapping components due to the six water molecules plus the OH groups. The band multiplicity observed in the low-wavenumber region ( −1 ) is compatible with the presence of two distorted PO 4 tetrahedra.

A suite of Ti-bearing garnets from magmatic, carbonatitic, and metamorphic rocks was studied by electron probe microanalysis (EPMA), X-ray powder diffraction (XRPD), single-crystal X-ray diffraction (SCXRD), Mossbauer spectroscopy, and secondary ion mass spectrometry (SIMS) to better characterize their crystal chemistry. The studied garnets show TiO 2 varying in the range of 4.9(1) to 17.1(2) wt% and variable Fe 3+ /∑Fe content. SIMS analyses allowed quantification of light elements yielding H 2 O in the range 0.091(7)–0.46(4), F in the range 0.004(1)–0.040(4), and Li 2 O in the range 0.0038(2)–0.014(2) wt%. Mossbauer analysis provided spectra with different complexity, which could be fitted to several components variable from one ( Y Fe 3+ ) to four ( Y Fe 2+ , Z Fe 2+ , Y Fe 3+ , Z Fe 3+ ). A good correlation was found between the Fe 3+ /∑Fe resulting from the Mossbauer analysis and that derived from the Flank method. X-ray powder analysis revealed that the studied samples are a mixture of different garnet phases with very close cubic unit-cell parameters as recently found by other authors. Single-crystal X-ray refinement using anisotropic displacement parameters were performed in the Ia 3 d space group and converged to 1.65 ≤ R 1 ≤ 2.09% and 2.35 ≤ wR 2 ≤ 3.02%. Unit-cell parameters vary in the range 12.0641(1) ≤ a ≤ 12.1447(1) A, reflecting different Ti contents and extent of substitutions at tetrahedral site. The main substitution mechanisms affecting the studied garnets are: Y R 4+ + Z R 3+ ↔ Z Si + Y R 3+ (schorlomite substitution); Y R 2+ + Z R 4+ ↔ 2 Y R 3+ (morimotoite substitution); Y R 3+ ↔ Y Fe 3+ (andradite substitution); in the above substitutions Y R 2+ = Fe 2+ , Mg 2+ , Mn 2+ ; Z R 4+ = Ti; Y R 3+ = Fe 3+ , Al 3+ , Cr 3+ ; Z R 3+ = Fe 3+ , Al 3+ . Minor substitutions, such as 2 Y Ti 4+ + Z Fe 2+ ↔ 2 Y Fe 3+ + Z Si, (SiO 4 ) 4− ↔ (O 4 H 4 ) 4− , F − ↔ OH − , and Y R 4+ + X R + ↔ Y R 3+ + X Ca 2+ , with Y R 4+ = Ti, Zr; Y R 3+ = Fe 3+ , Al, Cr 3+ ; X R + = Na, Li also occur.

This paper relates an infrared (IR) (6000–2500; 1400–400 cm–1) spectroscopic study of sideronatrite, Na2Fe3+(SO4)2(OH)·3H2O. Spectra in the 600–1250 cm–1 range are dominated by fundamental S–O absorption bands. Factor-group analysis based on the space group P212121(D42) is in accordance with the observed band multiplicity. A broad and convolute absorption centred around 3400 cm–1 and a sharp band at 3605 cm–1 are observed in the 2900–3900 cm–1 frequency region. The resolution of the broad band is significantly improved at liquid nitrogen temperature; seven components can be fitted to the pattern and these can be assigned to H2O/OH molecules in the structure. All components in the broad band and the sharp absorption at 3605 cm–1 are strongly polarized for E//a, in accordance with the structure analysis results. Infrared transmission spectroscopy is a useful tool to identify these sulfate minerals occurring in specific geological environments.