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A study of the morphology and evolution of the microstructure during thermal decomposition of Y2(C2O4)3·10H2O was conducted, and the stages and factors having the greatest impact on particle size and specific surface area were identified. The effect of the yttrium oxalate hexahydrate phases on the course of decomposition was also investigated. The evolution of the morphology and microstructure of decomposition products was explained from the analysis of volume shrinkage at various stages of the reaction. The formation of oxycarbonate is accompanied by the largest shrinkage during the reaction. At this stage, there is a significant increase in the specific surface area to 60–90 m2/g. Conversely, the morphology and microstructure of the particles during the transformation of oxycarbonate into yttrium oxide change insignificantly. Yttrium oxide powders obtained from the monoclinic and triclinic hexahydrate phases have the same specific surface area, but different morphology and bulk density due to pseudomorph formation. The carbon formed during thermolysis was shown to affect the specific surface area of the decomposition product. Two methods for producing yttrium oxide with high specific surface area have been proposed, and nanocrystalline yttrium oxide with a specific surface area of 65 m2/g was obtained.

The thermal-assisted exfoliation phenomena of boehmite particles under moderate heating rates were examined. The exfoliation that generated flakes of 5–6 nm in thickness can be achieved because of the perfect cleavage on the boehmite particles that are stripped when thermal treatments bring about dehydration and γ-Al2O3 formation in sequential phase transformation of boehmite. Examinations of the exfoliation effects were carried out on calcined boehmite single crystal particles, which were about 500 nm in diameter, and obtained at three heating rates 0.5, 1.0, and 2.0 °C/min with the heating schedules. The TEM techniques, BET-N2 measurements, XRD-Scherrer equation, and AFM images were employed in the examination. That the BET values increased as increasing of exfoliated flakes reflected two stages of exfoliation. In the beginning stage, during which the BET values were

This paper reports on an ice-wedge pseudomorph that formed and is preserved in metavolcanic host material that was later transformed to metamorphic solid bedrock. It has been dated to 1,895 ± 5 Ma by U–Pb geochronology of zircon in the bedrock, an Early Proterozoic age. Detailed observation of the deformation structures of the wedge points to an ice-wedge pseudomorph based on typical downbending around the wedge and vertical lamination in the inner part of the wedge due to slumping into the wedge after the ice melted, along with a few remains of lateral pressure structures (such as folds and upturned strata) in the adjacent host sediment. The interpretation of the wedge structure as an ice-wedge pseudomorph confirms previous work on this topic. This ice-wedge pseudomorph demonstrates for the first time the existence of permafrost at c. 1.9 Ga. It indicates that permafrost and associated conditions were present in lowlands at low latitude at discrete time intervals early in Earth’s history. Although some caution should be applied, mean annual air temperature appears to have been slightly below the freezing point at that time.

The paradigm for hydrous high-strain zones that cut dry host rocks is for fluid-rock interaction to have involved aqueous fluids. However, the role of silicate melt is increasingly recognised. This contribution examines the formation of glimmerite (biotitite) bands during melt migration in the Gough Dam shear zone, a high-strain zone in central Australia that was active during the Alice Springs Orogeny (c. 450–300 Ma). The glimmerite bands cut and replace a range of quartzo-feldspathic protoliths, including granitic gneiss and quartzite. Melt that migrated through the high-strain zone is interpreted to have penetrated relict layers along a network of fractures, enhancing dissolution of the precursor rock and causing replacement by glimmerite crystallisation. Microstructures indicative of the former presence of melt in the high-strain zone include: pseudomorphs of former melt pockets of granitic composition; small dihedral angles of interstitial phases; elongate grain boundary melt pseudomorphs; neighbourhoods of grains connected in three dimensions; and localised static grain growth and recovery. Other microstructures indicative of melt-present deformation include randomly oriented neosome grains, and evidence of activation of multiple slip systems during deformation. The degree of quartzite modification to glimmerite is recorded by an increase in biotite mode, and correlated with higher Ti concentrations in biotite (higher apparent temperature) and changes to trace element and REE compositions. Melt-assisted coupled dissolution-precipitation reactions during melt flux are interpreted to partially reset Proterozoic monazite U-Pb ages inherited from the protolith (> 1630 Ma) to younger Palaeozoic ages, with a complex age pattern partially congruent with the Alice Springs Orogeny (apparent ages range from c. 606–371 Ma, with a dominant age peak at c. 451 Ma). We propose that the glimmerite formed during dynamic melt migration of an externally-derived hydrous peraluminous melt, driving reaction replacement of various felsic protoliths during this orogenic event. Refereed/Peer-reviewed

National audience; Unlike most "wedge" orogens, the structure and the composition of theTibetan Plateau lower crust has kept being largely inaccessible otherwisethan by geophysical studies and by the few scattered sampling ofxenoliths brought to the surface by volcanism. In the Nangqian basin (NEQiangtangterrane), Eocene syn-contractional potassic lavas carrypartially molten foliated quartzo-feldspathic xenoliths. Zircon LA-ICPMSU-Pb dating of these crustal xenoliths yields a Lower Triassic age of ca.248.5 Ma, which is interpreted as the protolith crystallization age, withno evidence for any metamorphic zircon growth or resetting. The rarerelict ferro-magnesian minerals found (clinopyroxene, amphibole,phlogopite, garnet) are in textural and chemical disequilibrium, makingconventional thermobarometry methods inoperable. Nevertheless, thexenoliths have retained unusual metamorphic features which can helpunravelling their pre-entrapment metamorphic history. Pure anorthite"patches" with magnetite inclusions are interpreted as pseudomorphsafter garnet. Since these patches are often found in contact withclinopyroxene and rutile, these minerals may together represent a formerhigh-pressure assemblage that developed at 1.2-1.5 GPa and 620-730°C.Such pressure record would indicate that 80% of the present-day crustalthickness of the Tibetan Plateau was already acquired in Eocene times.Moreover, corundum-bearing assemblages, interpreted as pseudomorphsafter phlogopite, are best explained by kinetic disequilibrium underhigh-temperature granulitic conditions, suggesting a short-livedmetamorphic event. Taken together, this set of new petrological andgeochronological data suggests that crustal granulitic metamorphism maynot b e related to the onset of a general warming of the Tibetan crustsustained until the present, but rather to the punctual injection of mantlederivedmelts in the crust before Eocene eruption.

The detailed mineralogical and microgeochemical characteristics of polymetallic nodules collected from the Interoceanmetal Joint Organization (IOM, Szczecin, Poland) claim area, Eastern Clarion-Clipperton Fracture Zone (CCFZ, Eastern Pacific) were described in this study. The obtained data were applied for the delimitation of nodule growth generations and estimation of the growth ratios (back-stripping using the Co-chronometer method). The applied methods included bulk X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA), providing information about Mn-Fe minerals and clays composing nodules, as well as the geochemical zonation of the growth generations. The analyzed nodules were mostly diagenetic (Mn/Fe &gt, 5), with less influence on the hydrogenous processes, dominated by the presence of 10-Å phyllomanganates represented by todorokite/buserite, additionally mixed with birnessite and vernadite. The specific lithotype (intranodulith), being an integral part of polymetallic nodules, developed as a result of the secondary diagenetic processes of lithification and the cementation of Fe-rich clays (potentially nontronite and Fe-rich smectite), barite, zeolites (Na-phillipsite), bioapatite, biogenic remnants, and detrital material, occurs in holes, microcaverns, and open fractures in between ore colloforms. The contents of ∑(Ni, Cu, and Co) varied from 1.54 to 3.06 wt %. Several remnants of siliceous microorganisms (radiolarians and diatoms) were found to form pseudomorphs. The applied Co-chronometer method indicated that the nodules’ age is mainly Middle Pliocene to Middle Pleistocene, and the growth rates are typical of diagenetic and mixed hydrogenetic–diagenetic (HD) processes. Additionally, few nodules showed suboxic conditions of nucleation. Growth processes in the eastern part of the CCFZ deposit might have been induced with the Plio-Pleistocene changes in the paleooceanographic conditions related to the deglaciation of the Northern Hemisphere.

During phase transitions the ordering of cations and/or anions along specific crystallographic directions can take place. As a result, extra reflections may occur in diffraction patterns, which can indicate cell doubling and the reduction of the crystallographic symmetry. However, similar features may also arise from twinning. Here the nanostructures of a glendonite, a calcite (CaCO3) pseudomorph after ikaite (CaCO3·6H2O), from Victoria Cave (Russia) were studied using transmission electron microscopy (TEM). This paper demonstrates the occurrence of extra reflections at positions halfway between the Bragg reflections of calcite in 0kl electron diffraction patterns and the doubling of d104 spacings (corresponding to 2∙3.03 Å) in high-resolution TEM images. Interestingly, these diffraction features match with the so-called carbonate c-type reflections, which are associated with Mg and Ca ordering, a phenomenon that cannot occur in pure calcite. TEM and crystallographic analysis suggests that, in fact, (101¯4) calcite twins and the orientation change of CO3 groups across the twin interface are responsible for the extra reflections.

The Messinian lagoonal carbonate–evaporite sequence of Cyrenaica, north‐east Libya, hosts: (i) opaline nodules in gypsiferous microbial‐rich mudstone; (ii) nodules replacing poikilotopic gypsum cementing bioclastic carbonates; and (iii) bedded porcelanite with large lenticular gypsum pseudomorphs intercalated with recrystallized microbial mats. Optical microscopy, scanning electron microscopy, backscattered electron images – secondary electron images, X‐ray fluorescence, X‐ray diffraction and cathodoluminescence techniques were employed to elucidate on the early stages of chert diagenesis and demonstrate the role of moganite in the formation of varieties of chalcedony during silicification. The opaline nodules composed of opal‐A, exhibit shrinkage cracks lined by isopachous fibrous quartzine underlain by a thin birefringent zone. This suggests that quartzine may develop by crystallization and conversion of opal‐A through a transitional moganite. The quartzine is followed by amorphous silica gel that converts into length‐fast chalcedony. By contrast, lutecite evolved by silica replacement of gypsum through a transitional moganite phase, which forms an amorphous zone in apparent optical continuity with the fibrous lutecite; as moganite advances by pseudo‐crystalline terminations controlled by the gypsum cleavage. In gypsified oyster shells, intercrystalline organic matter enveloping pseudomorphed shell microstructures enabled moganite nucleation that merges syntaxially around the gypsum crystal rim. The associated lutecite occurs as radial‐fibrous beekite aggregates that are consistent with early shell silicification. The bedded porcelanite consists of opal‐CT groundmass undergoing recrystallization and enclosing micro‐cavities lined by quartzine. The associated pseudomorphs display phases of gypsum replacement by moganite and lutecite at the outer margin, followed by dissolution and cavity filling by quartz varieties in response to fluid flushing. In all cases, organic matter and microbes played a vital role in the silicification process.

The differentiation process of ultrapotassic magmas is enigmatic and poorly understood. The Yaojiazhuang ultrapotassic complex is concentrically zoned by late-intruded syenite in the core and early emplaced clinopyroxenite in the periphery, combining a “bi-modal” lithology. Spatially, apatite and iron oxide-apatite (IOA) ores, glimmerite and pseudoleucite occur in the upper part of clinopyroxenite. The syenite and clinopyroxenite are composed of variable amounts of clinopyroxenite, biotite, K-feldspar, magnetite, apatite with minor analcite, titanite, and primary calcite. The pseudoleucite clinopyroxenite contains mainly clinopyroxene, biotite and garnet in the matrix, and nepheline–K-feldspar intergrowth with muscovite and minor celestine in the leucite pseudomorph. Geochemically, rocks of the Yaojiazhuang complex are significantly enriched in potassium (K), light rare earth elements (LREE), and large ion lithophile elements (LILE). Crustal contamination by Archean tonalite–trondhjemite–granodiorite (TTG) gneisses basement may play an important role to convert the syenitic melts from silica-undersaturation to saturation. Fractionation crystallization is supported by the mineral crystallization sequence to explain the bimodal lithologies instead of silicate liquid immiscibility. During the magmatic evolution, decompression, fractionation of volatile-poor clinopyroxene and the enhancement by CO2 may result in the exsolution of an aqueous fluid. The late-stage interactions between existing minerals and magmatic fluids in the crystal mush could be a key process in the generation of both leucite pseudomorphs and apatite/IOA ores.

En el presente trabajo se estudian los procesos de carbonatación de frústulas de diatomeas y la consecuente formación de calizas/dolomías diagenéticas, en estratos de diatomitas marinas (Messiniense, sección de Níjar) y lacustres (Turoliense, sección de Tresjuncos). Se realiza un estudio mineralógico y petrológico para conocer el reemplazo de ópalo A por calcita o dolomita, considerando los factores que favorecen este reemplazo en ambos ambientes. Los datos obtenidos son relevantes para la investigación del uso de diatomitas en la captura y alma­cenamiento de dióxido de carbono a través de su carbonatación. Los procesos pseudomórficos de carbonatación de las valvas se llevaron a cabo mediante el reemplazo directo del ópalo A por calcita o dolomita y la cementación de la microporosidad. La perfecta reproducción de las valvas indica un mecanismo de reacción con acoplamiento de disolución-precipitación en la interfase de reacción. Se interpreta que la organización de las microesferas de ópalo A, dentro de las valvas, condicionaría la organización de complejos amor­fos de varios iones o nanopartículas de carbonatos amorfos, que posteriormente recristalizarían a calcita o dolomita. En las diatomitas lacustres, el proceso de carbonatación de las valvas fue favorecido por la materia orgánica proveniente de la gran cantidad de biota (anfibios, crustáceos, insectos, plantas... etc.) que incorporan. En este ambiente, los procesos de sulfato-reducción durante la degradación de la materia orgánica, generaron CO2, que junto con cambios de pH y salinidad facilitaron los reemplazos. Es posible que las carbonataciones de las valvas fueran coetáneas a la precipitación de calcita y dolomita que fosiliza la biota y por lo tanto, diagenéticas tempra­nas. En las diatomitas marinas, el proceso desencadenante del reemplazo de las valvas fue la formación de capas lenticulares y nódulos opalinos, ya que al disolverse los microfósiles calcáreos que las diatomitas incluían, se liberó CO2 y Ca. Pequeñas variaciones de pH en un entorno alrededor de 9, y la presencia de sulfatos facilitarían el reemplazado durante la diagénesis por enterramiento.

Eudialyte-hosted critical metal deposits potentially represent major sources of rare earth elements (REE), zirconium and niobium. Here, we study the chemical and isotopic composition of fresh and altered eudialyte in nepheline syenite from the Il&iacute, maussaq Complex, Greenland, one of the world&rsquo, s largest known eudialyte-hosted deposits. Late-magmatic hydrothermal alteration caused partial replacement of primary magmatic eudialyte by complex pseudomorph assemblages of secondary Zr-, Nb-, and REE-minerals. Three secondary assemblage types are characterised by the zirconosilicates catapleiite, gittinsite and zircon, respectively, of which the catapleiite type is most common. To investigate elemental exchange associated with alteration and to constrain the nature of the metasomatic fluids, we compare trace elements and Sm/Nd isotope compositions of unaltered eudialyte crystals and their replaced counterparts from five syenite samples (three catapleiite-type, one gittinsite-type, and one zircon-type assemblage). Trace element budgets for the catapleiite-type pseudomorphs indicate a 15&ndash, 30% loss of REE, Ta, Nb, Zr, Sr and Y relative to fresh eudialyte. Moreover, the gittinsite- and zircon-type assemblages record preferential heavy REE (HREE) depletion (&le, 50%), suggesting that the metasomatic fluids mobilised high field strength elements. Initial Nd isotope ratios of unaltered eudialyte and catapleiite- and gittinsite-type pseudomorphs are indistinguishable, confirming a magmatic fluid origin. However, a higher initial ratio and stronger HREE depletion in the zircon-type pseudomorphs suggests a different source for the zircon-forming fluid. Although alteration reduces the metal budget of the original eudialyte volume, we infer that these elements re-precipitate nearby in the same rock. Alteration, therefore, might have little effect on overall grade but preferentially separates heavy and light REE into different phases. Targeted processing of the alteration products may access individual rare earth families (heavy vs. light) and other metals (Zr, Nb, Ta) more effectively than processing the fresh rock.

Lacustrine stromatolites were widespread in the Miocene Wudaoliang Group (stromatolites of the Wudaoliang Group), northern Tibetan Plateau; but only at one location nearby the Wudaoliang Town, they occurred intensively in thick, laterally traceable beds (Wudaoliang stromatolites). Although deposited in lacustrine environment, the lack of fossils in these rocks hampers determining whether the stromatolites formed in freshwater or saline conditions. To address this problem, and in an attempt to identify criteria to distinguish differences of freshwater and saline conditions, we studied the laminae microfabrics, stable carbon and oxygen isotope ratios, rare earth element patterns and biomarkers of the stromatolites. These stromatolites can be divided into fenestral stromatolites and agglutinated stromatolites. The fabric of fenestral stromatolites is formed by microcrystalline carbonate enclosing spar-cemented, angular crystal traces. Essentially, this fabric is interpreted as pseudomorph after former formed evaporite crystals. Faecal pellets identical to that of the present-day brine shrimp Artemia, lack of other eukaryotic fossils, and stable isotopic signals point to a shallow, evaporation-dominated hypersaline lake setting. Covariation of carbon and oxygen isotopes indicates hydrologically closed conditions of the Miocene lake on northern Tibetan Plateau. However, if compared to other lacustrine carbonates of the Wudaoliang Group, the high δ13C values of the investigated Wudaoliang stromatolites reveal an additional photosynthetic effect during the deposition of the stromatolites. Furthermore, although no direct evidence is available from field observations and microfabrics, a positive europium anomaly of Wudaoliang stromatolites indicates that a palaeo-hydrothermal inflow system had existed in the outcrop area. These new results favour a hypersaline lake setting subject to hot spring inflow for the Wudaoliang stromatolites, in contrast to earlier interpretations suggesting a freshwater lake setting (e.g. Yi et al., Journal of Mineralogy and Petrology 28: 106–113, 2008; Zeng et al., Journal of Mineralogy and Petrology 31: 111–119, 2011). This approach may be appropriate for other lacustrine, unfossiliferous microbialites in settings where the environmental conditions are difficult to determine.

Celestite (SrSO4) single crystals immersed in highly concentrated Na2CO3 aqueous solutions (0.5 mol/l) are progressively pseudomorphised by aggregates of strontianite (SrCO3) crystals at ambient conditions. This replacement occurs by the coupling of dissolution and crystallisation reactions, eventually resulting in the formation of strontianite pseudomorphs, which reproduce the external shape of the initial celestite crystals. Experiments conducted for different reaction times indicate that the kinetics of the replacement reaction is mainly controlled by both the dissolution of the celestite substrate and the evolution of the porosity of the strontianite replacing layer. Such a porous layer allows the replacing solution to permeate towards the replacement front. During the initial stages of pseudomorph formation, the strontianite replacing layer is highly porous and the replacement front advances rapidly. As porosity decreases after a few days of reaction, the advancement of the strontianite replacement front slows down and an almost constant rate of about 0.3 µm/h is reached. Scanning electron microscope images and X-ray diffraction data have also shown that the growth of replacing strontianite aggregates occurs with a high degree of orientation with respect to the celestite substrate, i.e. the replacement is topotaxial., This work was partially supported by the Universidad Complutense-Comunidad de Madrid (Grant No. 910148-Superficies Minerales).

The extraordinary lateral continuity of isopachous stromatolite laminae in the ∼87 m-thick Mesoproterozoic Lakshanhatti Dolomite (India) evinces chemical precipitation. Fan-shaped crystals grown on lamina surfaces further corroborate this contention; growth of fan-shaped crystals under the overhanging stromatolite column-margin indicates direct carbonate precipitation from ambient waters. The fan-shaped crystals are stacked up, separated only by thin dark micritic laminae. In a relatively upper stratigraphic interval of the formation, lighter laminae characterized by a clotted texture and traversed by numerous winding tubular voids change gradually upwards into dark micritic laminae. Some sporadically distributed lenticular intraclastic beds also have the similarly dark micritic coatings. Clear carbonate cement crusts also occur between laminae and between successive dark micritic coats around intraclasts. Dull cathodoluminescence (CL) characterizes this cement as well as the cement lining within early diagenetic voids. In contrast, the laminae with clotted textures show dirty orange luminescence, while the dark micritic laminae and the dark micritic grain-coats display clear bright orange luminescence. Pyrite and its pseudomorphs are preferably concentrated along the dark micritic laminae. Carbon content in these dark micritic components, whether laminae or coats, is much higher than in the lighter components, exceeding what can be accounted for their CaMg(CO3)2 composition. A large part of this carbon is kerogen, plausibly biogenic. The dark components are, therefore, reasonably, though not unequivocally, assumed to be microbial mats. Degradation of the mats might have given rise to the light laminae with clotted textures. The fuzzy-margin tubes within the light laminae probably manifest the escape of gases generated during organic matter decomposition. Si–Al-rich terrigenous fines thinly draping the dark carbonaceous laminae was possibly the result of baffling and trapping of terrigenous fines by filamentous microbiota. Dark carbonaceous laminae encasing intraclasts was considered to be the result of binding and stabilization by microbiota. Spike-like growth of discrete laminae strongly suggests an occasional breakdown of colonial homeostasis of phototrophic microbiota. The microbial community thus appears to have played an active role in stromatolite-building in the Lakshanhatti Dolomite Member, even though the simultaneous existence of direct carbonate precipitates from sea water indicates a hybrid origin of these stromatolites. Resting on shelf sandstone and being capped by dark offshore shale, the Lakshanhatti Dolomite had been deposited in distal offshore, but not at the great depth, perhaps in an epeiric sea. Progressive deepening inhibited direct carbonate precipitation. δ13C and δ18O values suggest normal open marine salinity during deposition.

Die oberflächennahen Ablagerungen des Perm und Quartär im Westteil der Liether Kalkgrube sind intensiv periglaziär überprägt. Drei annähernd parallel verlaufende, bis zu mehr als 3 m tiefe und 0,5 m breite Eiskeil-Pseudomorphosen sind aufgrund der Ausbildung in den Zechstein-Aschen und -Kalken, der ungewöhnlichen Größe und der Vergesellschaftung mehrerer ähnlich großer Strukturen von besonderer Bedeutung. Ihre Entstehung lässt sich mit den spezifischen Standortfaktoren erklären. Eine feinkörnige Beschaffenheit des Wirtsgesteines bot gute Voraussetzungen für eine intensivere Frostwirkung, ebenso wie die Exposition der Zechstein-Aschen mit geringer Quartärbedeckung. Eine ungewöhnlich große mechanische Festigkeit der Zechstein-Aschen im Vergleich zu typischen norddeutschen Lockergesteinen begünstigte die Entstehung größerer Strukturen. Die Vergesellschaftung, die ähnliche Dimensionierung und ähnliche Orientierung der drei großen Eiskeile deuten auf einen Zusammenhang mit einer salinartektonischen Vorzeichnung hin. Die sedimentologisch-tektonische Struktur der halokinetisch überformten Zechstein-Ablagerungen bestimmte die äußere Geometrie der Eiskeile maßgeblich mit. Bei der Füllung hinsichtlich Struktur, Mächtigkeit der einzelnen Füllungsabschnitte, Bodenart und -farbe deuten sich zwei unterschiedliche Bildungsphasen an. Offenbar erfolgte bei zwei Strukturen eine randliche, einseitige Öffnung und Verfüllung. Die Strukturen stellen möglicherweise prä-weichselkaltzeitliche Bildungen dar., research

The crystal structure of shkatulkalite has been solved from the crystal from the Lovozero alkaline massif, Kola Peninsula, Russia. The mineral is monoclinic, P2/m, a = 5.4638(19), b = 7.161(3), c = 15.573(6) &Aring, &beta, = 95.750(9)&deg, V = 606.3(4) &Aring, 3, R1 = 0.080 for 1551 unique observed reflections. The crystal structure is based upon the HOH blocks consisting of one octahedral (O) sheet sandwiched between two heteropolyhedral (H) sheets. The blocks are parallel to the (001) plane and are separated from each other by the interlayer space occupied by Na1 atoms and H2O groups. The Na2, Na3, and Ti sites are located within the O sheet. The general formula of shkatulkalite can be written as Na5(Nb1&minus, xTix)2(Ti1&minus, yMn2+y)[Si2O7]2O2(OH)2&middot, nH2O, where x + y = 0.5 and x &asymp, y &asymp, 0.25 for the sample studied. Shkatulkalite belongs to the seidozerite supergroup and is a member of the lamprophyllite group. The species most closely related to shkatulkalite are vuonnemite and epistolite. The close structural relations and the reported observations of pseudomorphs of shkatulkalite after vuonnemite suggest that, at least in some environments, shkatulkalite may form as a transformation mineral species.

The Sierra de Cacheuta vein-type Se mineralization in the Mendoza Province predominantly consists of clausthalite, klockmannite, eskebornite, eucairite, and naumannite. These primary selenides formed in a fault zone, cutting through fine-grained trachytic host rock. Cross-sections perpendicular to the veinlets, polarized light microscopy, and scanning-electron microscopy, combined with electron-microprobe analysis, provide a record of the relationship between different crystallization and deformation events. Mineralization encompasses four episodes of fault formation (d1–d4): early zonal selenide crystallization (stage (I)); ductile deformation of the selenides (stage (II)); fault re-opening, fluid-mediated metal mobilization, metalliferous-fluid infiltration, and mineral precipitation (stage (III)); and subsequent alteration (stage (IV)). The Se vein originated from multiple injections of highly oxidized, metal-rich fluids. These low-T solutions (estimated max. temperature 100 °C, max. pressure 1 bar) possessed high to exceptionally high Se fugacities (log fSe2 between −14.5 and −11.2) that prevailed for most of the evolution of the deposit. The source of the Se and the accompanying metals (Cu, Ag, Pb, and Fe) is probably the neighboring bituminous shale. The deposition of Se minerals occurred when the oxidized metal-bearing solutions came in contact with a reductant, which caused the reduction of mobile selenate to immobile selenide or elemental Se. We identified several features that permit us to safely distinguish samples from Cacheuta from Argentinian Se deposits in the Province of La Rioja: (I) trachytic host rock fragments containing bitumen and TiO2 pseudomorphs after titanomagnetite; (II) early Co-rich and Ni-poor krut’aite (Co < 6.7 wt %, Ni < 1.2 wt %) partly replaced by clausthalite, umangite, klockmannite, eskebornite, Ni-poor tyrrellite (Ni < 2.7 wt %), Ni-poor trogtalite (Ni < 1.2 wt %), and end-member krut’aite and petříčekite; (III) lack of calcite gangue; and (VI) Se-bearing alteration minerals comprising chalcomenite, molybdomenite, cobaltomenite, an unnamed Cu selenide (for which the ideal formula may be either Cu2Se3 or Cu5Se8), and possibly mandarinoite, mereheadite, orlandiite, and scotlandite as new species for this occurrence.

At Kawah Ijen (Indonesia), vigorous SO2 and HCl degassing sustains a hyperacid lake (pH ~0) and intensely alters the subsurface, producing widespread residual silica and advanced argillic alteration products. In 1817, a VEI 2 phreatomagmatic eruption evacuated the lake, depositing a widespread layer of muddy ash fall, and sending lahars down river drainages. We discovered multiple types of opaline silica in juvenile low-silica dacite pumice and in particles within co-erupted laharic sediments. Most spectacular are opal-replaced phenocrysts of plagioclase and pyroxene adjacent to pristine matrix glass and melt inclusions. Opal-bearing pumice has been found at numerous sites, including where post-eruption infiltration of acid water is unlikely. Through detailed analyses of an initial sampling of 1817 eruption products, we find evidence for multiple origins of opaline materials in pumice and laharic sediments. Evidently, magma encountered acid-altered materials in the subsurface and triggered phreatomagmatic eruptions. Syn-eruptive incorporation of opal-alunite clasts, layered opal, and fragment-filled vesicles of opal and glass, all suggest magma-rock interactions in concert with vesiculation, followed by cooling within minutes. Our experiments at magmatic temperature confirm that the opaline materials would show noticeable degradation in time periods longer than a few tens of minutes. Some glassy laharic sedimentary grains are more andesitic than the main pumice type and may represent older volcanic materials that were altered beneath the lake bottom and were forcefully ejected during the 1817 eruption. A post-eruptive origin remains likely for most of the opal-replaced phenocrysts in pumice. Experiments at 25°C and 100°C reveal that when fresh pumice is bathed in Kawah Ijen hyperacid fluid for six weeks, plagioclase is replaced without altering either matrix glass or melt inclusions. Moreover, lack of evidence for high-temperature annealing of the opal suggests that post-eruption alteration of pumice is more likely than pre-eruption envelopment of euhedral opal-replaced phenocrysts in dacitic melt. At Ijen and elsewhere, the ascent of magma into hydrous acid-altered mineral assemblages (e.g., opal, kaolinite, alunite) could induce rapid dehydration of hydrous minerals and amorphous materials, generating considerable steam and contributing to magmatic-hydrothermal and phreatomagmatic explosions.

The study of the mechanisms by which mineral fibres promote adverse effects in both animals and humans is a hot topic of multidisciplinary research with many aspects that still need to be elucidated. Besides length and diameter, a key parameter that determines the toxicity/pathogenicity of a fibre is biopersistence, one component of which is biodurability. In this paper, biodurability of mineral fibres of social and economic importance (chrysotile, amphibole asbestos and fibrous erionite) has been determined for the first time in a systematic comparative way from in vitro acellular dissolution experiments. Dissolution was possible using the Gamble solution as simulated lung fluid (pH = 4 and at body temperature) so to reproduce the macrophage phagolysosome environment. The investigated mineral fibres display very different dissolution rates. For a 0.25 μm thick fibre, the calculated dissolution time of chrysotile is in the range 94–177 days, very short if compared to that of amphibole fibres (49–245 years), and fibrous erionite (181 years). Diffraction and SEM data on the dissolution products evidence that chrysotile rapidly undergoes amorphization with the formation of a nanophasic silica-rich fibrous metastable pseudomorph as first dissolution step whereas amphibole asbestos and fibrous erionite show minor signs of dissolution even after 9–12 months.

In this paper, we present a comparative study of the pseudomorphic carbonatation of gypsum and anhydrite single crystals in Mg-bearing aqueous solutions at room temperature. We have found that carbonatation of gypsum an anhydrite occurs via a similar coupled dissolution–crystallization mechanism. However, whereas pseudomorphization of anhydrite precisely preserves the external form and dimension of the initial crystals, pseudomorphs after gypsum are less perfect and the shape and volume of the original crystals are partially lost. Furthermore, the mineralogical compositions of the pseudomorphs after anhydrite and gypsum are different, because gypsum is replaced by relatively large calcite crystals, while anhydrite pseudomorphs consist of aggregates of calcite and aragonite. Such textural and compositional differences can be clearly related to the length scale of the coupling between dissolution and crystallization at the replacement fronts. In situ atomic force microscopy observations of the early stages of carbonatation have shown that dissolution and crystallization are very tightly coupled on anhydrite rather than on gypsum surfaces. This clearly indicates that during the replacement of anhydrite and gypsum, dissolution and precipitation, respectively, are the rate-limiting steps. On the other hand, the higher supersaturation levels reached during the replacement of anhydrite lead to a competition between calcite and aragonite crystallization. This explains the fact that calcite and aragonite coexist within the replacement layers after anhydrite. Finally, we have found that dissolved magnesium in the reacting solutions is almost equally incorporated into the pseudomorphs, regardless of both the precursor phase and the mineralogical composition of the replacements. Our calculations and chemical analyses have shown that the compositions of the MgxCa1–xCO3 solid solution for which supersaturations reach maximum values correspond quite well with maximum Mg/Ca ratios in the replacement layers., This work was supported by the Spanish Government (MAT2012-38810 and CGL2013-48247-P). AFM and SEM images, and EDX analyses were obtained at the ICTS Centro Nacional de Microscopia Electrónica-UCM. We thank Ana Vicente for assistance with the SEM. GIXRD patterns were recorded at the X-ray Diffraction Central Service-UCM. We also thank Ignacio Carabias for technical support and valuable help in GIXRD interpretation. C.P. is grateful to the Spanish Government for a FPU Fellowship.

Unusual speleothems, associated with hyperalkaline (pH > 12) groundwaters have formed within a shallow, abandoned railway tunnel at Peak Dale, Derbyshire, UK. The hyperalkaline groundwaters are produced by the leaching of a thin layer (3-type groundwaters and degassing of CO2. Stalagmites within the Peak Daletunnel have grown rapidly (averaging 33 mm y–1), following the closure of the tunnel 70 years ago. They have an unusual morphology comprising a central sub-horizontally-laminated column of micro- to nano-crystalline calcium carbonate encompassed by an outer sub-vertical assymetricripple-laminated layer. The stalagmites are composed largely of secondary calcite forming pseudomorphs (3·6H2O), withminor volumes of small (

Anatolia's high-pressure metamorphic belts are characterized in part by a Neotethyan stratigraphic succession that includes a mid-Cretaceous hemi-pelagic marble sequence. This unit contains, towards its stratigraphic top, dm-to-m-long radiating calcitic rods forming rosette-like textures. Here, we refer to these features as "Rosetta Marble". The remarkable textural similarity of non-metamorphic selenite crystals and radiating calcite rods in the Rosetta Marble strongly suggests that these textures represent pseudomorphs after selenites. Metamorphosed hemi-pelagic limestones, dominated by Rosetta selenite pseudomorphs, are alternating with siliceous meta-sediments containing relictic radiolaria tests. This stratigraphic pattern is indicative of transient phases characterized by evaporites precipitated from basinal brines alternating with non-evaporative hemi-pelagic deposition from normal-marine seawater. The regional distribution of Rosetta Marble exposures over 600 km is indicative of basin-scale evaporitic intervals. High-pressure, low-temperature metamorphism of these rocks is witnessed by Sr-rich (up to 3500 ppm), fibrous calcite pseudomorphs after aragonite and isolated aragonite inclusions in quartz. Peak metamorphic conditions of 1.2 GPa and 300-350 A degrees C are attested by high-Si white mica thermobarometry. The Rosetta Marble case example examines the potential to unravel the complete history from deposition to diagenesis and metamorphism of meta-sedimentary rocks.

Curly malachite (CM) is found as a green cupric carbonate hydroxide corrosion product on archaeological bronze, mostly on artefacts retrieved from graves. In this paper, a morphological characterization approach is proposed, enabling the investigation of the formation process of CM. It is suggested that curly malachite precipitates from an aqueous solution, for which the surrounding soil conditions provide local triggers. Anthropic activities associated with ritual burials do not significantly affect the growth of CM. It is also confirmed that curly malachite is usually not a pseudomorph of formerly organic material. Although the understanding of the formation process is far from complete, this study has shown that CM is expected to be found more often than is currently recognized, due to its relatively simple formation mechanisms and boundary conditions.

At Bangriposi, variable stages in replacement of staurolite by chloritoid - Na-K-Ca mica shimmer aggregates in muscovite schists provides insight into the complex interplay between fluid flow, mass transfer, and dissolution-precipitation during pseudomorph growth. Idioblastic chloritoid growing into mica caps without causing visible deformation, and monomineralic chloritoid veins (up to 300 mu m wide) within shimmer aggregates replacing staurolite attest to chloritoid nucleation in fluidfilled conduits along staurolite grain boundaries and crystallographic planes. The growth of shimmer aggregates initiated along staurolite margins, and advanced inwards into decomposing staurolite along networks of crystallographically controlled fluid-filled conduits. Coalescence among alteration zones adjacent to channel fills led to dismemberment and the eventual demise of staurolite. Mass balance calculation within a volume-fixed, silica-conserved reference frame indicate the shimmer aggregates grew via precipitation from fluids in response to mass transport that led to the addition of H2O, K2O, Na2O and CaO in the reaction zone, and Al2O3 was transported outward from the inward-retreating margin of decomposing staurolite. This aided precipitation of chloritoid in veins and in the outer collars, and as disseminated grains in the shimmer aggregates at mid-crustal condition (similar to 520 +/- 20 degrees C, 5.5 +/- 2.0 kbar). Computation using one-dimensional transport equation suggests that staurolite decomposition involved advection dominating over diffusive transport; the permeation of externally derived H2O caused flattening of chemical potential gradients in H2O and aqueous species, for example, (Na+H-1+] and [Na+ K--1(+1)], computed using the Gibbs method. This suggests that staurolite decomposition was promoted by the infiltration of a large volume of H2O that flattened existing chemical potential gradients. In the initial stages of replacement, chloritoid super-saturation in fluid caused preferential nucleation and growth of chloritoid at staurolite grain boundaries and in crystallographic planes. As reaction progressed, further chloritoid nucleation was halted, but chloritoid continued to grow as the 3-mica aggregates continued to replace the remaining staurolite in situ, while the chloritoid-compatible elements were transported in the water-rich phase facilitating continued growth of the existing chloritoid grains.

Curly malachite (CM) is found as a green cupric carbonate hydroxide corrosion product on archaeological bronze, mostly on artefacts retrieved from graves. In this paper, a morphological characterization approach is proposed, enabling the investigation of the formation process of CM. It is suggested that curly malachite precipitates from an aqueous solution, for which the surrounding soil conditions provide local triggers. Anthropic activities associated with ritual burials do not significantly affect the growth of CM. It is also confirmed that curly malachite is usually not a pseudomorph of formerly organic material. Although the understanding of the formation process is far from complete, this study has shown that CM is expected to be found more often than is currently recognized, due to its relatively simple formation mechanisms and boundary conditions.

The textural evolution in the serpentinite of the Mineoka ophiolite complex has been investigated to constrain the natural environment for hydrogen production in the serpentinite-hosted hydrothermal vent systems. Textural relations of the serpentinites from the Mineoka ophiolite indicate at least two stages in the process of serpentinization, with the replacement of olivine by a mesh texture of serpentine and brucite, followed by the development of magnetite-bearing or -free serpentine veins. The generation of hydrogen during serpentinization, which accompanies the formation of magnetite, involves a silica-depletion reaction, as evidenced by the low abundance of serpentine in the magnetite-bearing veins and the absence of magnetite in pseudomorphs of orthopyroxene. Direct evidence for the production of hydrogen and strongly reducing conditions is provided by CH4 and H-2-bearing inclusions in relic olivine crystals; the production of methane and hydrogen may have provided a suitable environment for microbial activity in hydrothermal vent systems along the seafloor. Our results indicate that low silica activity plays a key role in the generation of hydrogen during serpentinization, and that low silica activity environments are possible in olivine-rich rocks such as dunite, or during local disequilibrium in other silica-poor rocks in the mantle lithosphere.

Two new mineral species, trinepheline (NaAlSiO 4 ) and fabriesite (Na 3 Al 3 Si 3 O 12 · 2H 2 O), are described from late-stage metamorphic veins of the jadeite deposit of Tawmaw-Hpakant (Myanmar). Both minerals and their names were approved by the IMA Commission on New Minerals and Mineral Names (IMA 2012–024 and IMA 2012–080). The name trinepheline is known in literature for the polymorphs of synthetic NaAlSiO 4 with a value of the c parameter that is three times that of nepheline. Fabriesite is named in memory of Jacques Fabries (1932–2000), former professor of the “Museum National d’Histoire Naturelle” in Paris (France). Fabriesite and trinepheline occur intimately intergrown together with nepheline, more rarely with albite and other feldspar-group phases such as banalsite and stronalsite; other associated minerals are jadeite and secondary products like natrolite and harmotome. All phases have been identified via electron backscatter diffraction (EBSD) patterns. Both fabriesite and trinepheline are pseudomorph after jadeite and occur as skeletal allotriomorphic crystals up to 15–20 μm long and 5–10 μm wide. They are white to yellowish in hand specimen, colourless in thin section; the streak is white and the lustre appears vitreous to greasy; they are non-fluorescent; Mohs’ hardness is 5–5½. Empirical formulae (EMPA analysis) are very close to the ideal compositions with traces of Ca and K for trinepheline, and of Ca, K, Ba, Mg, Fe, and Mn for fabriesite. Calculated densities are 2.642 g cm −3 for trinepheline (space group P 6 1 , a = 9.995 A, c = 24.797 A) and 2.386 g cm −3 for fabriesite (space group Pna 2 1 , a = 16.426 A, b = 15.014 A, c = 5.223 A), respectively. The strongest five lines in the calculated X-ray powder diffraction patterns [ d (A) ( I )( hkl )] are: 3.163(100)(122), 3.834(81)(023), 4.133(49)(006), 3.272(40)(120) and 2.403(31)(127) for trinepheline; 3.41(100)(240), 4.41(77)(201), 2.97(70)(421), 2.61(40)(002) and 8.21(36)(200) for fabriesite.

Interpreting the origin of carbonate breccias requires a detailed analysis because they may be the result of a wide variety of processes that produce similar features. This is the case of the Lower Cretaceous carbonate breccias of the Cameros Basin (previously interpreted as slump or collapse breccias), whose origin is interpreted after performing a detailed sedimentary, petrographic and tectonic study. The studied carbonate breccias consist of angular carbonate mudstone fragments floating in a matrix of calcite and quartz crystals. The breccias are interbedded with, and laterally associated to, alternating layers of carbonate mudstone and calcite and quartz pseudomorphs after gypsum, which show strong similirities to the breccia fragments and matrix, respectively, suggesting that the brecciated beds were originally composed of identical alternating carbonate mudstone and gypsum layers as the unbrecciated layers. The breccias are associated with frequently polyharmonic deformation structures, which are similarly oriented as the regional tectonic structures, indicating that they are related with the alpine contractional deformation of this area of the Cameros Basin. All these features suggest that the carbonate breccias were formed by tectonic deformation of alternating layers of carbonate mudstone and calcium sulphate, which have very different rheological behaviours. As a result, during tectonic deformation, sulphate flowed and carbonate layers were broken and displaced, producing a breccia of carbonate fragments within a sulphate groundmass. Afterwards, the sulphate groundmass was replaced by quartz and calcite, and the breccia acquired its final composition.

Pseudomorphs of barite (BaSO4) and Cd-rich ZnS after whewellite (CaC2O4·H2O) occur within remnants of Scots pine bark tissues in the peat layer of a poor fen located near a zinc smelter in south Poland. A two-step formation of the pseudomorphs is postulated based on SEM observations: (1) complete dissolution of whewellite, possibly caused by oxalotrophic bacteria, and (2) subsequent bacterially induced precipitation of barite and spheroidal aggregates of ZnS together with galena (PbS) in voids left by the dissolved whewellite crystals. Local increase in pH due to microbial degradation of whewellite, elevated concentrations of Zn(II) and Ba(II) in pore water due to the decomposition of atmospheric particles of sphalerite and barite in the acidic (pH 3.5–3.8) environment, oxidation of S species during drying and rewetting of the peat layer, and subsequent partial reduction of sulfate anions by sulfur-reducing bacteria were all factors likely involved in the crystallization of ZnS and barite in the microenvironment of the post-whewellite voids.