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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.

Secondary weathering microstructures such as oxide rims, oxide veins and pseudomorphs of the weathering products are genetically related to altered (weathered) iron-nickel grains (kamacite α-(Fe,Ni), taenite γ-(Fe,Ni), plessite α+γ-(Fe,Ni)) of the Gruz’ke ordinary chondrite (H4). Rare microglobules of corrosion products were found in the hollow space inside some pseudomorphs. Various weathering microstructures consist of the dispersed mixtures of secondary iron oxyhydroxides – wide-spread goethite α-FeO(OH) and hydrogoethite FeO(OH)·nH2O. They spread from the grain boundary into the interior of the metal grains. The presence of lepidocrocite γ-FeO(OH) is assumed. Iron hydroxides are characterized by: а) heterogeneous grey color; b) various structures, the presence of replaced areas of mottled, collomorphic and layered structure; c) porosity and zonal structure; d) variations in the FeO and NiO content. The oxide rim around a large grain of Fe-Ni metal consists of (the average content from 4 an., content limits are given in the brackets, wt. %): FeO 82.7 (81.6–83.8); NiO 10.9 (10.4–11.7); SO3 4.88 (4.23–5.92); CoO 0.79 (up to 1.31); CuO 0.14 (up to 0.57); MnO 0.14 (up to 0.54); MgO 0.16; K2O + CaO 0.13; Cl 0.17 (up to 0.26). Iron oxyhydroxide pseudomorph contains (the average of 3 an., limits – in the brackets. wt. %): FeO 92.6 (92.1–93.0); NiO 3.5 (2.72–4.02); SiO2 3.86 (3.32–4.96); Cl 0.08 (up to 0.24). The phase and chemical heterogeneity of Fe-Ni, low Ni concentration in α-(Fe,Ni) are the main causes of selective oxidation and replacement of kamacite and plessite, compared to taenite. The process of corrosion and replacement of Fe-Ni metal occurred in the presence of moisture, as evidenced by the direct spatial connection of iron-nickel with FeO(OH)·nH2O. Completely altered Fe-Ni grains, which have lost their primary structural and chemical characteristics, are not quite reliable for the interpretation of the pre-terrestrial processes of the meteorite matter formation. Iron hydroxides have a low chlorine content of Cl < 0,3 wt. %, which indicates their low corrosiveness. As a result, further corrosion and replacement of the Fe-Ni metal will be inhibited, which will prevent oxidation of the meteorite sample during laboratory research and storage.

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. [ABSTRACT FROM AUTHOR]

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 <40 m2/g, the exfoliation resulted from the stress produced by dehydration. In the second stage, the increased rate of surface area was due to the additional force, which originated from the γ-Al2O3 formation. Exfoliation occurred on the cleavage planes {010}, the side pinacoid of the boehmite particle. The generation of flakes resulted in the thinning of boehmite particles. Some of the flakes preserved the external form of boehmite crystals. From the surface energy evaluations of boehmite and γ-Al2O3, it can be inferred that exfoliation is a natural way of thermal treatment. [ABSTRACT FROM AUTHOR]

This paper presents a historical perspective of the discovery of, and aspects of, glendonite and ikaite, through the legacy of British mineralogists Douglas Shearman and Alec K. Smith. Much of the knowledge, literature review and synthesis presented in the following paper raises from the original work and discussions that these two key figures in mineralogy shared with the geological community both in the form of their official communications but also as informal discussions with the first author. Through our extensive review, we show that, while the link between ikaite and glendonite is now undeniable, questions remain. [ABSTRACT FROM AUTHOR]

The Blue Lace Agate mine exploited a hydrothermal vein deposit at Ysterputs in southern Namibia until 2017. The deposit occupies a shear zone and associated fractures in a Jurassic dolerite sill that intruded a Permian marine deposit. Much of the chalcedony constituting the agate is the length-slow variety 'quartzine', indicating deposition in a saline environment, presumably derived from the marine sediments. Associated minerals are dolomite, forming an initial coating on the fissure wall and brecciated dolerite fragments, as well as late-stage crystals of ankerite, calcite, dolomite, gypsum and quartz. Ysterputs is also the source of cubic chalcedony pseudomorphs, originally thought to be after fluorite, but probably after melanophlogite. • Chemical results of the minerals of the blue lace agates from Ysterputs in southern Namibia, including calcite and dolomite. • Micrographs of the length-slow 'quartzine' in agate, believed to originate from marine sediments of the Whitehill formation. • Presence of cubic chalcedony pseudomorphs, probably after melanophlogite. [ABSTRACT FROM AUTHOR]

Replacement reactions occur during metamorphism and metasomatism in response to changes in pressure, temperature and bulk rock and fluid compositions. To interpret the changes in conditions, it is necessary to understand what phases have previously been present in the rocks. During fluid-mediated replacement, the crystallography of the replacement phases is often controlled by the parent reactant phase. However, excessive fluid fluxing can also lead to extreme element mobility. Titanium is not mobile under a wide range of fluid compositions and so titanium-bearing phases present an opportunity to interpret conditions from the most extreme alteration. We map orientation relationships between titanium-bearing phases from ore deposits using EBSD and use symmetry arguments and existing relationships to show that completely consumed phases can be inferred in ore deposits. An ilmenite single crystal from Junction gold deposit is replaced by titanite, rutile and dolomite. The rutile has the following well-documented orientation relationship to the ilmenite [0001]ilmenite // < 100 > rutile and < 10 1 ¯ 0 > ilmenite // [001]rutile The anatase is a single crystal and shows a potential orientation relationship [0001]ilmenite = (0001)ilmenite // {211}anatase and < 10 1 ¯ 0 > ilmenite // < 0 1 ¯ 1 > anatase The single crystal orientation and lack of symmetrical equivalent variants suggest nucleation dominates the anatase production. Dolomite grew epitaxially on the ilmenite despite only sharing oxygen atoms suggesting the surface structure is important in dolomite nucleation. Titanite partially replaced ilmenite during metasomatism at Plutonic gold deposit. The titanite orientation is weakly related to the ilmenite orientation by the following relationship: [0001]ilmenite // < 100 > titanite and { 10 1 ¯ 0 }ilmenite // (001)titanite The prevalence of subgrain boundaries in the titanite suggests multiple nucleation points on an already deformed ilmenite needle leading to the formation of substructure in the absence of deformation. Existing known topotaxial replacement relationship can be used to infer completely replaced phases using the misorientation distributions of the replacement polycrystals. Orientation modelling for a cubic phase replaced by rutile in a sample from Productora tourmaline breccia complex shows misorientation distributions consistent with < 001 > Rutile // < 110 > cubic and < 100 > Rutile // < 111 > cubic Combining this with volume constraints and assuming Ti is immobile, the composition of the cubic phase is constrained as titanomagnetite with 85% ulvospinel. Complex microstructures with domanial preferred orientations can also be used to document the microstructure of replaced phases. An aggregate of rutile grains with two parts that share a common < 100 > axis is interpreted as having replaced a twinned ilmenite grain. Modelling shows that the misorientation distribution for the aggregate is consistent with the above relationship replacing ilmenite with a { 10 1 ¯ 2 } twin. [ABSTRACT FROM AUTHOR]

The characteristic inking behaviour of cephalopods is a secondary defence mechanism that helps them to escape predation. However, although it has been postulated that ink creates a decoy by disrupting the visual information received by the predator, the underlying mechanisms by which ink helps squid to escape from predators remain unknown. Therefore, we observed the inking behaviour of the Japanese pygmy squid (Idiosepius paradoxus). Field observations showed the squid intermittently and linearly ejected ink while rapidly swimming backwards in response to a predator and also changed their bodies to a light colour. This behaviour was then followed by a sudden and sharp change in swimming direction or sometimes a sudden break from swimming with a concurrent change in body colour to black. We also recorded the escape behaviour with inking under captive conditions in response to predatory sculpins, which allowed the successful escape from a predatory attack. Furthermore, the greater the number of ink ejections, the higher the probability that the sculpins would initiate a predatory attack on the ink rather than the squid. Together, these results suggest that squid inking behaviour exhibits a substantial decoy effect on predators and is associated with a series of complex, spatio-temporally regulated behaviours. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo200107ip01a, http://www.momo-p.com/showdetail-e.php?movieid=momo200107ip03a, and http://www.momo-p.com/showdetail-e.php?movieid=momo200107ip04a. [ABSTRACT FROM AUTHOR]

Coronae between olivine and plagioclase are a common replacement texture in mafic rocks by magmatic and metamorphic processes. Mafic dykes from Palghat Cauvery Shear Zone (PCSZ) of the granulite terrane of southern India display such multilayer coronae between olivine (Ol) and plagioclase (Pl), composed of orthopyroxene-magnetite (OM) and amphibole (Prg). Deformation twins, kinking, bending and fractures in plagioclase laths suggest that the rock underwent post-emplacement deformation. However, amphibole in the plagioclase fractures and preservation of delicate coronae texture indicate that the replacement texture grew in a static condition. Field occurrence and textural relations suggest that the coronae developed in two stages: (1) Stage-I: Ol → OM, followed by (2) Stage-II: OM + Pl = Prg during rehydration of the granulite host rock. Balanced chemical reactions and formation of hydrous amphibole at the expense of anhydrous reactants during Stage-II demonstrates that replacement of earlier minerals occurred in a fluid-present open system. Results from the pseudosection and the μMgO–μCaO phase diagram, suggest fluid played a crucial role in the transition from Stage-I to Stage-II corona at a P-T condition of ~650 ± 50 °C and 5.5–6 kbar. The multilayer coronae is likely to have resulted from late Neoproterozoic thermal metamorphism of granulite terrane of southern India during Pan-African orogeny. [ABSTRACT FROM AUTHOR]

Syros is part of the Attic–Cycladic blueschist belt and consists principally of marbles, schists, and metabasites that have been metamorphosed to the blueschist- to eclogite-facies at about 52 Ma, with a greenschist-facies overprint beginning at about 25 Ma. Distinct, whitish clusters of sub-millimeter-sized grains organized into orthorhombic polyhedral shapes occur in a variety of the blueschists. These clusters are interpreted to be pseudomorphs after lawsonite based on their shape, chemistry, and the presence of rare relict lawsonite in a few of the clusters. A considerable range in observed pseudomorph modes reflects both variety in rock compositions and the extent of greenschist overprinting. Most pseudomorphs contain epidote-group minerals (clinozoisite/epidote), similar to the composition of ideal lawsonite, except for added Fe and lost water. Many contain white mica (phengite, paragonite, muscovite), which requires the addition of K and/or Na to the original lawsonite. In some cases, the pseudomorph is largely mica, so that Ca must have been lost to an epidote mineral, amphibole, or calcite in the matrix. Phengite in the pseudomorphs typically has a lower celadonite content than phengite in the matrix. It appears that the mica has changed its composition by breakdown in the matrix, K diffusion, and regrowth in the pseudomorph. We propose that lawsonite breakdown must be in part driven by the reaction of lawsonite with the celadonite content of phengitic mica in the matrix, to form celadonite-poor (muscovite-rich) white mica in the pseudomorph. The preservation of the lawsonite shape in the pseudomorphs in weakly deformed rocks appears to be due to the relative immobility of Al during the pseudomorphing reactions, with K, Na, and Fe moving to the pseudomorphs and Ca and H2O leaving. The only source of K in these rocks is phengite, which should become less rich in celadonite with an increase in temperature, needed to drive lawsonite breakdown. [ABSTRACT FROM AUTHOR]

Abstract Carbonate apatite (CO 3 Ap) is an inorganic component of mature bone and is used as bone substitute instead of autografts. Recently, 100% pure CO 3 Ap granules formed from calcium carbonate via a dissolution-precipitation reaction have been used as a clinical precursor for bone. In this study, the feasibility of fabricating blocks of CO 3 Ap from blocks of octacalcium phosphate (OCP), which is an analog of the bone composition and serves as a precursor for bone, was investigated by immersion in NaHCO 3. The macroscopic structure of the OCP block was retained upon conversion to CO 3 Ap. In addition, as the NaHCO 3 concentration increased from 0.0 to 2.0 mol/L, the carbonate content increased in the resulting CO 3 Ap, reaching ≈ 14 wt% at maximum NaHCO 3 concentration. Moreover, the morphology of the CO 3 Ap crystals varied as the NaHCO 3 concentration increased up to 0.5 mol/L: they were pseudomorphic plate-like when the NaHCO 3 concentration was low but formed particles ranging ~ 10 nm in size at high NaHCO 3 concentrations. The different phase transformation modes depended on NaHCO 3 concentrations closely related to CO 3 Ap crystal morphology and were associated with a decrease in the mechanical strength of the block. Graphical abstract Different phase conversion modes from OCP to CO 3 Ap depended on CO 3 concentration fx1 [ABSTRACT FROM AUTHOR]

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 6 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.

High-pressure serpentinites from Alpine Corsica, the Piedmont Zone (Western Alps), the Tso Morari dome (Himalaya), the Dominican Republic and Cuba (Greater Antilles) contain reddish (Ni,Fe)-rich silicate aggregates, a few hundred micrometers in size, which have not been reported so far from lower-pressure serpentinites, nor found there through systematic screening. The high atomic (Ni+Fe)/Si ratio (5+4) of these aggregates, as well as their occurrence as coronas around (Ni+Fe)-sulfides, indicates their formation at the expense of sulfides and serpentine. The high (Ni+Fe)/Si ratio may suggest the presence of an Fe or Ni analogue of the rare serpentine-related minerals balangeroite or cronstedtite. However, compositional variations within and between aggregates, synchrotron X-ray diffraction data acquired on single aggregates, and transmission electron microscopy reveal that these aggregates are not a single phase but rather a mixture at the hundreds of nanometer scale of oxyhydroxides, mainly goethite (FeOOH)+(Ni,Fe)-rich serpentine±chlorite±reevesite [Ni6Fe2(OH)16(CO3).4H2O]±magnetite. In addition to microtexture and mineralogy, strong chemical variations at the border of the aggregates and along micro-veins suggest formation through a low-temperature alteration process. However, the occurrence of such pseudomorphic aggregates only in high-pressure serpentinites suggests that they were formed at the expense of a high-pressure silicate precursor of high M2+/Si ratio, still to be identified but which could be a main nickel carrier at depth in subduction zones. [ABSTRACT FROM AUTHOR]

The Precambrian granulite facies rocks of Lindås Nappe, Bergen Arcs, Caledonides of W. Norway are partially hydrated at amphibolite and eclogite facies conditions. The Lindås Nappe outcrops over an area of ca. 1000 km 2 where relict granulite facies lenses make up only ca. 10%. At Hillandsvatnet, garnetite displays sharp hydration fronts across which the granulite facies assemblage composed of garnet (55%) and clinopyroxene (45%) is replaced by an amphibolite facies mineralogy defined by chlorite, epidote and amphibole. The major element bulk composition does not change significantly across the hydration front, apart from the volatile components (loss on ignition, LOI) that increases from 0.17 wt.% in the granulite to 2.43 wt.% in the amphibolite. However the replacements of garnet and of clinopyroxene are pseudomorphic so that the grain shapes of the garnet and clinopyroxene are preserved even when they are completely replaced. The textural evolution during the replacement of garnet by pargasite, epidote and chlorite and of pyroxene by hornblende and quartz in our rock sample conforms to that expected by a coupled dissolution–precipitation mechanism. SEM and electron microprobe analysis coupled with the software XMapTools V 1.06.1 were used to quantify the local mass transfer required during the replacement processes. The element losses and gains in replacing the garnet are approximately balanced by the opposite gains and losses associated with the replacement of clinopyroxene. The coupling between dissolution and precipitation on both the grain and whole rock spatial scale preserves the volume of the rock throughout the hydration process. However, the hydration involves reduction of rock density and mass balance calculations, together with volume preservation (isovolumetric reaction) require a significant loss of the mass of the rock to the fluid phase. This suggests a mechanism for coupling between the local stress generated by hydration reactions and mass transfer, dependent on the spatial scale over which the system is open where the fluid infiltration is pervasive along grain boundaries. [ABSTRACT FROM AUTHOR]

Recrystallization of zircons under the influence of fluids was studied using examples from Precambrian rocks (microcline granites, metasedimentary, and mafic rocks) of the Kola Peninsula. All zircon crystals showed complex internal textures visible by cathodoluminescence and backscattered electron (BSE) imaging. Detailed mineralogical and geochemical studies with subsequent secondary ion mass spectrometer U–Pb dating of different zircon domains show that secondary texture formation can be interpreted in terms of metasomatic replacement of zircon crystals on the base of crystallogenetic experimental models. Mechanisms of zircon replacement and interpretation of U–Pb ages for secondary zircon domains are dependent on the degree of damage of the zircon structure and the fluid composition. The recrystallization of metamict zircon without additional supply of new zircon substance (Zr, SiO2) goes with the dissolution of amorphous domains and precipitation of new polycrystalline zircon, which preserves the U–Pb initial age, but loses radiogenic lead, and the lower intercept of Discordia lines with the Concordia curve determines the time of fluid influence. The recrystallization of metamict zircon or crystalline zircon with high contents of impurities with additional supply of Si and Zr forms monocrystalline replacements. Dissolution of primary zircon is accompanied by growth of new zircon domains differing in the composition of isomorphic impurities and zones of transitional composition, whose ages have no geological sense. The study is of particular importance for zircons from Precambrian rocks with long and complex histories. [ABSTRACT FROM AUTHOR]

A numerical approach is developed to simulate the formation of pseudomorphs with presence of chemical fluids at the mesoscopic scale. This approach consists of the lattice Boltzmann method (LBM) for transport of chemical species in the pore space, a chemical reaction model including basic kinetics of the coupled dissolution and precipitation reactions, and a mesoscopic model for nucleation and crystal growth. Our study confirms the mechanism of the solution chemistry-driven interface-coupled dissolution-precipitation for the formation of pseudomorphs and identifies several sources for the generation of porosity in the pseudomorphs. We demonstrate that epitaxial precipitation is not necessary and random crystal growth may be more favorable for pseudomorphs. We show that the difference of precipitation barrier on the surface of the primary and secondary minerals should not be too large. Otherwise only the rim of the primary phase is roughly preserved. [ABSTRACT FROM AUTHOR]

Fibre products, such as textiles and animal pelts, are often recovered in the corrosion crust of archaeological metal artefacts. Because clothed burials are an important resource for the study of past societies, accurate fibre identification is important. However, extreme mineralisation of animal fibres can render microscopic visualisation difficult for species identification. Peptide mass fingerprinting (PMF) has been successfully used to identify the species origin in both collagen and keratin-made archaeological artefacts. The approach requires little material but the state of degradation (protein hydrolysis) is a limiting factor as it might impact on the identification of key markers. In this study we analysed pelt and textile fragments found in association with copper-alloy objects with different degrees of mineralisation; samples were obtained from a Viking-Age (10th c.) grave in Britain and from a burial in Mongolia (3rd c. BC to 2nd c. AD). Species identification was possible in all but one sample, revealing PMF can be applied to corrosion products, thereby further expanding the value of these objects for textile research. [ABSTRACT FROM AUTHOR]

Abstract: Wood ash, composed mainly of the mineral calcite, is an important component in many archaeological sites. Identification of wood ash in the archaeological record is often difficult due to mixing of ash with other calcitic components of geogenic origin and/or due to diagenetic changes. A recent empirical study using the stable isotope compositions of carbon (δ13C) and oxygen (δ18O) in wood ash enabled the identification of mixtures of wood ash with geogenic calcite and to follow diagenetic changes due to partial dissolution and re-precipitation of ash in two prehistoric cave sites in Israel. Little however is known about the processes responsible for the isotopic compositions of wood ash in relation to formation at various temperatures and the influence on isotopic composition of ash from a variety of plant species. Here we present an experimental study of wood ash formed by burning three C3 tree species and one C4 desert bush at different temperatures. The results indicate that there are significant differences in the isotopic compositions of carbon and oxygen between wood ash that forms by combustion at a relatively low temperature (500 °C) and at a higher temperature (900 °C). In addition, we show that the isotopic composition of carbon and oxygen in high temperature wood ash approaches equilibrium over a period of several months and that the carbon isotopic composition of low temperature wood ash may reflect the photosynthetic pathway of the burnt woody species. Lastly, we show that the isotopic compositions obtained from wood ash prepared at different temperatures do not reflect a temperature dependent fractionation process, but a mixing line between calcite that formed by low temperature combustion and calcite formed by high temperature combustion which later underwent re-carbonation with atmospheric CO2. In addition, we suggest that exchange processes may possibly occur during combustion between decomposing calcium-oxalate and atmospheric O2, CO2 and CO. The archaeological implications of this study are discussed in relation to identification of wood ash in the archaeological record, identification of fuel sources and burning temperatures, and diagenetic changes expected in karstic cave environments. The method presented here can be applied at any archaeological site. [Copyright &y& Elsevier]

Numerous rod-shaped calcite crystals occur in the blueschist to eclogite facies marbles of Syros, Greece. The rods show a shape-preferred orientation, and the long axes of the rods are oriented at a large angle to foliation. The crystals also have a crystallographic-preferred orientation: calcite c-axes are oriented parallel to the long axes of the rods. Based on their chemical composition, shape, and occurrence in high-pressure marbles, these calcite crystals are interpreted as topotactic pseudomorphs after aragonite that developed a crystallographic-preferred orientation during peak metamorphism. This interpretation is consistent with deformation of aragonite by dislocation creep, which has been observed in laboratory experiments but has not been previously reported on the basis of field evidence. Subsequent to the high-pressure deformation of the aragonite marbles, the aragonite recrystallized statically into coarse rod-shaped crystals, maintaining the crystallographic orientation developed during deformation. During later exhumation, aragonite reverted to calcite, and the marbles experienced little further deformation, at least in the pseudomorph-rich layers. Some shearing of pseudomorph-bearing marble layers did occur and is indicated by twinning of calcite and by a variable inclination of the pseudomorphs relative to foliation. [Copyright &y& Elsevier]

The 370–380 Ma Khibina and Vuoriyarvi complexes on the Kola Peninsula, Russia, which form part of the Palaeozoic Kola Alkaline Province, contain REE-rich carbonatites with burbankite (Na,Ca)3(Sr,Ca,REE,Ba)3(CO3)5 or calcioburbankite (Na,Ca)3(Ca,Sr,REE,Ba)3(CO3)5 as the principal primary REE mineral. Within each complex the C–O and Sr–Nd isotopic data are similar for burbankite group minerals and co-existing calcite or dolomite (Khibina: δ13C(V-PDB)=−6.4 to−5.8‰, δ18O(V-SMOW)=7.3–7.7‰, (87Sr/86Sr)370=0.70390–0.70404 and (143Nd/144Nd)370=0.51230–0.51235; Vuoriyarvi: δ13C=−4.2 to −3.0‰, δ18O=8.1–9.4‰, (87Sr/86Sr)370=0.70313–0.70315 and (143Nd/144Nd)370=0.51243–0.51245). This indicates that the REE mineralization and its host carbonatites in each complex are derived from the same source and are co-genetic. There is, however, a great difference between the Sr, Nd and C isotopic signatures from Khibina and Vuoriyarvi, whereas the δ18O ranges are similar. This suggests that the REE carbonatites of the two complexes originate from sources with different isotopic signatures. At least three mantle components are needed to explain the variations in Sr and Nd compositions in the carbonatites from Kola. The δ13C ranges of primary carbonatites with low δ18O values are quite different for Khibina and Vuoriyarvi and show correlation with the radiogenic isotope compositions. The data may be best explained by subduction-related source contamination that caused δ13C variations in different mantle components. During late-stage processes burbankite and calcioburbankite have been replaced by various assemblages of REE–Sr–Ba minerals. The alteration of burbankite group minerals is an open-system hydrothermal process leading to multiple element transfer. It has produced mineral assemblages which are characterized by high δ18O values (Khibina: δ18O(V-SMOW)=11.4–13.9‰ and Vuoriyarvi: δ18O=17.1–18.0‰) compared to primary burbankite and calcioburbankite. Co-existing calcite and dolomite have retained their original C and O isotope compositions, and one calcite sample from Khibina shows strong positive δ13C–δ18O shifts similar to those of the pseudomorph. The high δ18O and sometimes high δ13C values can be attributed to low-temperature isotope exchange between minerals and fluid with variable CO2/H2O ratio taking place during and/or after crystallization as usually observed in carbonatites. The Sr and Nd isotope compositions of pseudomorphs and associated calcite/dolomite in general are identical to those of burbankite/calcioburbankite and associated carbonates suggesting that the fluids which caused burbankite alteration are from the same source, i.e. carbonatitic. Small variations in the Sr and Nd isotope signatures point to interaction of the pseudomorph-forming fluid with alkali silicate wall rocks. [Copyright &y& Elsevier]

During metamorphism, evidence of the prograde path is commonly obliterated by continued recrystallization as temperatures increase. However, prograde pseudomorphs that are common in many terrains may provide insight into this portion of the metamorphic path if their mineralogy can be accurately interpreted. Seventeen sillimanite-zone metapelitic samples, each containing 2-5 muscovite-rich pseudomorphs, from the Farmington Quadrangle, Maine, U.S.A., were investigated to evaluate their use as indicators of conditions during prograde metamorphism. SEM-CL images, X-ray maps, image analysis, and electron microprobe analyses characterize the mineral distribution, modes, and compositions within the pseudomorph and the surrounding matrix. Based on modal mineralogy determined from image analyses, the muscovite-rich pseudomorphs are divided into four major types: muscovite-rich (>70% muscovite), quartz-muscovite (60-70% muscovite with 10-25% quartz), plagioclase-muscovite (58-72% muscovite with 10-20% plagioclase), and sillimanite-plagioclase-muscovite (50-60% muscovite with 10-20% each plagioclase and sillimanite). A biotite-rich, muscovite-poor mantle surrounds many pseudomorphs. All pseudomorphs are interpreted to be prograde, based on their texture, and are after staurolite because of the partial replacement of staurolite by coarse muscovite at lower grades. Textural modeling of reaction mechanisms required to reproduce the observed mineralogy in the pseudomorphs indicates that each major pseudomorph type holds clues to the prograde path and represents a different mechanism of formation. Muscovite-rich and quartz-muscovite pseudomorphs formed by the breakdown of staurolite containing different modal amounts of poikiloblastic quartz. Quartz-muscovite pseudomorphs likely reflect a quartz-rich initial rock composition. Plagioclase-muscovite pseudomorphs require the infiltration of Na-bearing fluids. Sillimanite-plagioclase-muscovite pseudomorphs require a two-stage process; the infiltration of Na-rich fluids during staurolite breakdown followed by sillimanite growth. The subtle mineralogical differences recorded in the pseudomorphs studied here provide evidence of previously unrecognized controls along the prograde path during metamorphism. [ABSTRACT FROM AUTHOR]