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Lithium (Li), a leading cathode material in rechargeable Li-ion batteries, is vital to modern energy storage technology, establishing it as one of the most impactful and strategical elements. Given the surge in the electric car market, it is crucial to improve lithium recovery from its rich mineral deposits using the most effective extraction technique. In recent years, both industry and academia have shown significant interest in Li recovery from various Li-bearing minerals. Of these, only extraction from spodumene has established a reliable industrial production of Li salts. The current approaches for cracking of the naturally occurring, stable α-spodumene structure into a more open structure—β-spodumene—involve the so-called decrepitation process that takes place at extreme temperatures of ~1100 °C. This conversion is necessary, as β-spodumene is more susceptible to chemical attacks facilitating Li extraction. In the last several decades, many techniques have been demonstrated and patented to process hard-rock mineral spodumene. The objective of this review is to present a thorough analysis of significant findings and the enhancement of process flowsheets over time that can be useful for both research endeavors and industrial process improvements. The review focuses on the following techniques: acid methods, alkali methods, carbonate roasting/autoclaving methods, sulfuric acid roasting/autoclaving methods, chlorinating methods, and mechanochemical activation. Recently, microwaves (MWs), as an energy source, have been employed to transform α-spodumene into β-spodumene. Considering its energy-efficient and short-duration aspects, the review discusses the interaction mechanism of MWs with solids, MW-assisted decrepitation, and Li extraction efficiencies. Finally, the merits and/or disadvantages, challenges, and prospects of the processes are summarized. [ABSTRACT FROM AUTHOR]

The value of gem opals is compromised by their potential susceptibility to "crazing", a phenomenon observed either in the form of whitening or cracking. To understand the latter, 26 opal samples were investigated and separated into 2 groups based on handling: "water-stored" opal samples, which are stored in water after extraction, and "air-stored" opal samples, which are stored in air for more than a year. To induce cracking, samples were thermally treated by staged heating and characterized using optical microscopy and Raman spectroscopy before and after cracking. For water-stored opals, cracking was initiated with moderate heating up to 150 °C, while for air-stored opals, higher temperatures, circa 300 °C, were required. In water-stored opals that cracked, polarized light microscopy revealed stress fields remaining around the cracks, and a red shift in the Raman bands suggested tensile stresses. These stresses were not observed in air-stored samples that cracked. Based on these observations, for air-stored samples, cracking was ascribed to super-heated water-induced decrepitation. By contrast, for water-stored samples, cracking was linked to drying shrinkage, which correlates with the anecdotal reports from the gem trade. We thus identify the physical origin of cracking, and by comparing it to current knowledge, we determine the factors leading to cracking. [ABSTRACT FROM AUTHOR]

[Display omitted] • Computed tomography of kimberlitic melt inclusions in ilmenite and olivine megacrysts. • Primary capture of melt near the base of the continental lithosphere. • Raman spectroscopy indicates the preservation of Mg-rich H 2 O-CO 3 bearing glass. Ilmenite and olivine megacrysts from the 89 Ma Monastery kimberlite (Kaapvaal Craton, South Africa) captured abundant and large melt inclusions containing quenched Si-Mg-rich melt, calcite, spinel, perovskite, phlogopite, and serpentine. Textural observations and 3D X-ray tomography of ilmenite and olivine megacrysts show melt inclusion shapes, sizes and distribution patterns indicative of melt capture during primary crystal growth near the base of the subcontinental lithospheric mantle (SCLM). Patterns supporting secondary melt injection along fractures or veins, such as planar arrays of melt inclusions, are absent. Melt inclusions in olivine, in some examples reaching the dimension of centimetres, likely were captured in skeletal voids forming in fast growing, up to decimetre-sized olivine megacrysts. These large melt inclusions commonly decrepitated, forming apophyses, radial fractures, and veins, along which residual volatile- and Si-Mg-rich melt was extracted. We attribute the decrepitation of melt inclusions in olivine to the rapidly increasing difference between the melt pressure in the inclusions, captured at mantle depth, and the decreasing confining stress to which the host olivines were exposed during magma ascent and after emplacement. In ilmenite, melt inclusions up to ∼ 6 mm in diameter remained commonly intact during the kimberlite ascent from its mantle source to the shallow crust. The quenched silicate melt in olivine- and ilmenite-hosted melt inclusions, in some places preserved as unaltered hydrous and CO 3 -bearing glass, shows systematic major element compositional variations that suggest that this melt formed by similar fractionation and depletion processes, irrespective of the hosting megacryst phase. Apparent modal variations in quenched silicate melt, calcite, and oxide contents suggest that the melt batches captured as inclusions in ilmenite and olivine either record different evolution stages in the megacryst magma, or document compositional heterogeneities in this magma at the time of megacryst growth. [ABSTRACT FROM AUTHOR]

Manganese ores are the major raw materials utilized in the production of manganese ferroalloys. A common problem in the production of manganese ferroalloys is the lack of knowledge regarding mineralogical and metallurgical properties of manganese ores. Decrepitation, which is described as the breakage or disintegration of the ore particles upon heating, is an important quality parameter of these ores. The decrepitation Index (DI), which is the parameter used to describe the extent of decrepitation, is described as the ratio of mass of particles

Recently, the demand for lithium metal and its associated compounds has been growing exponentially, mainly due to the increased consumption of lithium ion batteries. Consequently, to meet this demand, minerals such as spodumene have become the most important lithium-bearing resources. Although numerous methods have been studied for the extraction of lithium from spodumene, the conventional process of spodumene decrepitation followed by leaching in sulfuric acid, remains the proven commercial process. In the high temperature decrepitation process, α-spodumene is converted into β-spodumene and also some intermediate γ-spodumene can form. In the current research, a comprehensive thermodynamic analysis of the decrepitation of spodumene has been performed using HSC Chemistry® 7.1. Firstly, the thermodynamic data available in the literature for the various relevant lithium aluminosilicates was evaluated and then this data was incorporated into the HSC data base. Secondly, using the experimental data available in the literature, the non-ideal behaviour of spodumene was accounted for by the incorporation of activity coefficients. Finally, the model was applied to the decrepitation of both pure spodumene and also a spodumene concentrate. The modelled conversion results were in good agreement with the process data available in the literature. [ABSTRACT FROM AUTHOR]

The present study deals with the modeling of a single intermetallic powder particle likely to form reversibly a hydride material while submitted to hydrogen gas. These materials that make part of the so-called hydrogen solid storage family are one of the most employed media used in order to store hydrogen. During hydrogenation cycling, the initially coarse powder expanses due to hydrogen absorption and shrinks over hydrogen desorption. The powder granularity also decreases with the number of cycles but seems to stabilize to reach a mechanical limit. One plausible explanation is that large particles decrepitate into smaller ones because, only due to their geometry, they are less able to accommodate large volume changes and thus, internal stresses are higher than in small particles. This is the hypothesis we intend to discuss in the present work, hypothesis that has never been investigated, in our knowledge, from a mechanical point of view. Within the framework of a simple analytical model, several parameters (initial particle size, material behavior parameters ...) are varied in order to evaluate their influence on the propensity of the particle to decrepitate. After introducing the context, the model that allows describing the fragile elastic mechanical response of a single spherical particle submitted to hydrogen is presented. Computed stress and strain along the radius of particles with different size or elastic properties lead to the main conclusion: considering a spherical particles made of an undamaged uniform elastic brittle two phase material is insufficient to evidence dependency of the mechanical response on the particle size. Consequently, this primary model is unable to validate our hypothesis, according which the limit size of decrepitating is driven by the mechanical accommodation of volume changes. This implies that a description of heterogeneities or geometric irregularities must be introduced to account for the phenomenon of particle size stabilization during decrepitating. After results are presented and discussed, opportunities to deepen the present analysis are proposed to account for physical observations of the decrepitating phenomenon, and are to be developed in forthcoming publications. Image 1 • Investigations on decrepitation during hydrogen absorption in metal hydride. • Special attention to the modeling of absorption/desorption in a spherical particle. • Study deals with the mechanical description during phase transformation. • Continuum mechanics framework does not predict the limit size of particles. [ABSTRACT FROM AUTHOR]

The Earth's mantle holds more carbon than its oceans, atmosphere and continents combined, yet the distribution of carbon within the mantle remains uncertain. Our best constraints on the distribution of carbon within the upper mantle are derived from the carbon-trace element systematics of ultra-depleted glasses and melt inclusions from mid-ocean ridge basalts. However, carbon-trace element systematics are susceptible to modification by crustal processes, including concurrent degassing and mixing, and melt inclusion decrepitation. In this study we explore how the influence of these processes varies systematically with both the mantle source and melting process, thereby modulating both global and local carbon-trace element trends. We supplement the existing melt inclusion data from Iceland with four new datasets, significantly enhancing the spatial and geochemical coverage of melt inclusion datasets from the island. Within the combined Iceland dataset there is significant variation in melt inclusion C/Ba ratio, which is tightly correlated with trace element enrichment. The trends in C/Ba-Ba space displayed by our new data coincide with the same trends in data compiled from global ocean islands and mid-ocean ridges, forming a global array. The overall structure of the global C/Ba-Ba array is not a property of the source, instead it is controlled by CO 2 vapour loss pre- and post-melt inclusion entrapment; i.e., the array is a consequence of degassing creating near-constant maximum melt-inclusion carbon contents over many orders of magnitude of Ba concentration. On Iceland, extremely high C/Ba (> 100) and C/Nb (> 1000) ratios are found in melt inclusions from the most depleted eruptions. The high C/Ba and C/Nb ratios are unlikely to be either analytical artefacts, or to be the product of extreme fractionation of the most incompatible elements during silicate melting. Whilst high C/Ba and C/Nb ratios could be generated by regassing of melt inclusions by CO 2 vapour, or by mantle melting occurring in the presence of residual graphite, we suggest the high values most likely derive from an intrinsically high C/Ba and C/Nb mantle component that makes up a small fraction of the Icelandic mantle. [ABSTRACT FROM AUTHOR]

• Quartz sand is rich in fluid inclusions, which are natural thermometers in concrete. • After fire, the highest temperature experienced concrete can be analysed. • Inclusion decrepitation thermoacoustic thermometry is stable and reliable. • The relative error of inclusion decrepitation thermoacoustic thermometry is <10 %. The fire-exposure temperature of concrete directly determines the degree of damage to its microstructure and the performance of concrete. Therefore, an accurate assessment of the fire-exposure temperature of concrete is crucial. But to date, there is not yet an accurate, practical, and effective method for measuring the internal temperature of concrete after fire. Based on the discovery that fluid inclusions in concrete act as natural thermometers, this paper investigates the scientific principles and experimental evidence of the decrepitation thermometry of inclusions. By extracting quartz sand samples from the interiors of concrete members after a fire and performing an inclusion decrepitation test on these samples, the maximum fire-exposure temperature of concrete can be determined with a high degree of accuracy. The test results reveal that the natural sand used in construction typically contains fluid inclusions, indicating that the necessary conditions for inclusion decrepitation thermometry are satisfied for concrete structures. In this study, standard quartz sand samples were configured, and inclusion decrepitation temperature measurements were conducted after subjecting the samples to different heating rates, cooling methods, thermostatic durations, and standing times after fire. The test results indicate that the impact of the aforementioned factors on the inclusion decrepitation temperature measurement is not evident. The maximum relative error between all temperature measurement results and the actual heating temperature is <10 %, and the average relative error is <2.5 %. The experimental results show that fluid inclusions are natural thermometers in concrete. After a fire, the maximum temperature experienced in the concrete can be quantitatively assessed using the initial decrepitation temperature of the inclusion. This method possesses the advantages of being a scientific test method and providing accurate temperature measurements without any indirect analysis or calculation using simple test equipment, sample preparation, and operation. [ABSTRACT FROM AUTHOR]

Recycling of Nd-Fe-B magnets is one of the few solutions to alleviate the supply risks of certain rare earth elements (REE) such as Nd and Dy. One of the most promising solutions with regards to extraction of end-of-life (EOL) magnets is to apply hydrogen decrepitation and to physically separate the Nd-Fe-B as a demagnetized hydrogenated powder. Such a powder can be directly recycled into new sintered magnets, or indirectly recycled by a conventional oxidation roasting and acid leaching flowsheet. The oxidation stability of powders, the microstructure after oxidation and the role of compositional variations can be of importance for the success of such subsequent direct or indirect recycling routes. In this study, magnets with varying compositions were subjected to different hydrogen treatments (e.g. hydrogenation, partial or full degassing and vacuum or conventional disproportionation) and subsequently studied for their comparative oxidation behavior and microstructural changes. While initial magnet composition was found to have little or no effect on oxidation behavior, the treatment type was found to have a direct impact on both the particle size distribution and the oxidation mechanism. The general oxidation rate was found to be the equally highest for hydrogenated and partially degassed samples followed by fully degassed and then disproportionated samples. After complete oxidation, complex REE-Fe-O compounds were formed more extensively in hydrogenated and fully degassed NdFeB samples than in the disproportionated samples. [ABSTRACT FROM AUTHOR]

Trace Na sources, extraction dynamics of trace Na, and influences of calcination temperature on quartz lattice, fluid inclusions, and muscovite were studied in detail herein for trace Na extraction from the quartz ore with water leaching at 90°C. Experimental results suggested that the trace Na sources included quartz lattice, fluid inclusions, and muscovite. The extraction rate of the trace Na in quartz ores can reach 31.0wt% after calcination at 900°C for 5 h and water leaching at 90°C for 24 h. The extraction process consisting of the dissolution of unfree Na and diffusion of free Na was dominated by calcination temperature. Calcination at 900°C for 5 h was effective for extraction of the trace Na in fluid inclusions and muscovite. The extraction of the trace Na was mainly affected by the decrepitation of fluid inclusions when the calcination temperature ranged from 400 to 600°C and by the damage of muscovite when the calcination temperature ranged from 600 to 900°C. Based on the extraction rates at different calcination temperatures, approximately 20.1wt% of the trace Na occurred in fluid inclusions, approximately 10.9wt% existed in muscovite, and 69.0wt% mainly occurred in quartz lattice. [ABSTRACT FROM AUTHOR]

The decrepitation of two Chinese lump coals was investigated using high-temperature fast pyrolysis in a purpose-designed furnace to simulate the reaction conditions in the coal-based Corex ironmaking process, and evolution of functional group, porosity, crystallite structure as well as CO2 reactivity of resultant coal chars was characterized. The results demonstrate that the decrepitation index varied significantly for different coal samples and their particle sizes, because of the variable thermal stress induced. The decrepitation index increased with increasing temperature and particle size, and severe decrepitation was observed when coal particles were increased to 20 mm. The coal chars derived from Xinglongzhuang lump coal at different temperatures had much more developed macroporous structure than Datong lump coal chars. A significant change of the crystallite height demonstrated a great influence of temperature on carbon structure. The CO2 reactivity of coal chars decreased with increasing annealing time at different temperatures examined, but the effect of carbonization temperatures on their reactivity has the opposite behavior, which is related to the porosity development and carbon structure variation. The interrelations of these phenomena further suggest that the appropriate dome temperature is crucial for ensuring permeability of coal char bed in Corex except for coal type. Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Using x-ray phase, chemical, and thermal (20-1200°C) analysis methods, phase composition and thermal properties are evaluated for three specimens of quartz-containing materials used as fluxes in copper smelting production. It is established that quartz in specimens on heating to 1000-1200°C undergoes enantiothropic polymorphic transformation by a scheme: α-quartz → β-quartz → β-cristobalite. In order to evaluate the efficiency of using materials as fluxes for copper smelting production, equations are proposed for calculating fluxing capacity depending on their chemical and phase composition. A dependence is given for the amount of slag formed as a result of slagging flux impurity oxides on material phase and chemical compositions on whose basis losses of nonferrous and precious metals are evaluated. It is suggested that flux materials are heated to a temperature for the start of polymorphic transformations accompanying quartz recrystallization (~560°C) before charging into a metallurgical unit. [ABSTRACT FROM AUTHOR]

In this study, effects of mechanical activation on the thermal characteristics of colemanite (Ca 2 B 6 O 11 ·5H 2 O) were examined with respect to its decrepitation behavior observed during the heating processes. Mechanical activation was achieved by milling (up to 150 min) in a planetary ball mill using tungsten carbide milling media. Crystallinity of the milled colemanite samples was determined by performing X-ray powder diffraction analysis. In this manner, milling conditions at which crystalline colemanite transforms to amorphous structure were obtained. Thermal gravimetric (TG) analyses together with differential thermal (DTA) and differential thermogravimetric (DTG) analysis were performed to determine how prolonged milling affects the thermal behavior of colemanite. It was found by examining the DTA data that intensive milling gives rise to removal of the crystal water from colemanite at low temperatures, which can be attributed to mechanical activation. DTG analysis revealed that mechanical activation decreases the rate of water removal from colemanite structure throughout the heating. It was suggested that mechanical activation eliminates the decrepitation almost completely, so that there is no need for pre-calcining operation which is generally required before manufacturing the colemanite-based high temperature materials. [ABSTRACT FROM AUTHOR]

Fine generation during thermal processing (basically roasting) of oxide materials is an unattained issue due to lack of knowledge on the mechanism of particle breakage. An important quality parameter to quantify fine generation for lumpy oxide materials is decrepitation. In this research article, primary reasons for decrepitation of polyformic materials like manganese oxides are addressed by characterization and experiments followed by a theoretical model for particle breakage. Herein, the physical, chemical and mineralogical characterizations of low grade manganese ore lumps from Indian mines are presented. Particle breakage has been correlated with the heat profile in the porous bed for three different packing geometries by variation of parameters: heating rate, time, and temperature. Optimization analysis was performed using response surface methodology to estimate the effect of interaction parameters on fine generation and to estimate the optimum parameter setting with a maximum of 5% fine generation. Secondly, a mathematical model was developed to simulate the heat transfer behavior in a single particle of 6 mm diameter with the objective of moisture evaporation and to estimate the heat distribution in porous bed geometries. Finally, a thermo-mechanical stress model has been developed to support the mechanism of particle breakage. Heat transfer analysis shows that cylindrical bed geometry has better heat distribution due to less bed permeability and larger contact area between the particles. The optimized condition for roasting of low grade manganese ores to achieve transformation of manganese dioxide & up to 5% decrepitation is as follows: temperature:700 °C, heating rate: 10 °C/min, and roasting time: 70 min. [ABSTRACT FROM AUTHOR]

This study investigates the upgrading possibilities of the tailings of Eti Maden Bigadiç Boron concentration plant. Firstly, it was planned to compose a pre-concentrated product by way of clay removal from tailing in the experimental studies. The tailing samples have been tested by attrition scrubbing method in a constant stirring rate and in the several pulp densities. From these tests, a pre- concentrate containing 23.78% B2O3 grade was produced. The decrepitation experiments were applied on the pre-concentrate to profit from the disintegration of colemanite minerals by heating in order to obtain a higher grade concentrate. As a result of the decrepitation tests, a concentrate containing 45.57% B2O3 grade was obtained with a recovery of 88.47% B2O3. [ABSTRACT FROM AUTHOR]

The paper presents the selected results of the thermal decomposition of natural magnesite for preparation of active MgO. At the temperature of selective decomposition of magnesite intermediate phases exhibiting enhanced reactivity and low mechanical stability are formed. Evolution of carbon dioxide is accompanied by decrepitation of active magnesia. The selective decomposition and the accompanying decrepitation of the solid may be conveniently used as a way of enriching the chemically active magnesia by simple screening. Magnesia is accumulated in the undersize fraction, whereas undecomposed calcium carbonate and silica remain in the oversize fractions.

Many energy-related materials rely on the uptake and release of large quantities of ions, for example, Li+ in batteries, H+ in hydrogen storage materials, and O2− in solid-oxide fuel cell and related materials. These compositional changes often result in large volumetric dilation of the material, commonly referred to as chemical expansion. This article reviews the current knowledge of chemical expansion and aspires to facilitate and promote future research in this field by providing a taxonomy for its sources, along with recent atomistic insights of its origin, aided by recent computational modeling and an overview of factors impacting chemical expansion. We discuss the implications of chemical expansion for mechanical stability and functionality in the energy applications above, as well as in other oxide-based systems. The use of chemical expansion as a new means to probe other materials properties, as well as its contribution to recently investigated electromechanical coupling, is also highlighted. [ABSTRACT FROM AUTHOR]

The manganese lump ore from Morro da Mina mine is typically silicate carbonated and presents a great economic potential for the ferroalloy companies installed in Minas Gerais. However, its low manganese content, associated with the lack of knowledge about its metallurgical properties makes it difficult for large scale application. This pioneering study aimed to amply investigate this lump ore's particle disintegration. One ton of ore from the mine was homogenized and quartered. Representative samples were characterized by different techniques, such as ICP-AES, XRD, SEM, BET and OM. Aiming to characterize particle disintegration, three parameters were proposed: Cold Disintegration Index (CDI), Decrepitation Index (DI) and Heating Disintegration Index (HDI). By using these indexes, it was possible to conclude that this manganese lump ore did not present significant disintegration at room temperature. At medium temperature test, slight decrepitation occurred, and at high temperatures, intense disintegration was detected. The carbonate decomposition and porosity growth were the main responsible factors for the ore hot particle disintegration. [ABSTRACT FROM AUTHOR]

The decrepitation activity of selected carbonate and sulphide minerals, as well as baryte was studied and it is presented in this paper. The thermal-vacuum impulse method was selected to be used for such a study within the thermal range of 25 400°C. It was confirmed that this method is also suitable for carbonate minerals with a medium decrepitation activity, e.g. magnesite with a fast transition from a non-impulse degasification to the impulse one. In case of very intensive decrepitating baryte mineral, the temperature of decrepitation is 60 70°C. The decrepitation activity of pyrite is lower at the temperature of 290 300°C as compared with arsenopyrite at the temperature of 150 170°C.If generalising the obtained results, it is necessary to note that the different decrepitation activity prefers the interpretation of mechanism of mineralogical school. The knowledge of the chemistry of solid phase extends the application possibilities of decrepitation of minerals in ceramics and drying processes.In connection with the technical conditions of drying process, it is significant that there is a limiting granularity with a minimal to zero decrepitation, while the temperature of drying is significantly decreasing. This information is based on the results obtained by technical-analytical study of dolomite minerals and coal.

Manganese ores are the major raw materials utilized in the production of manganese ferroalloys. A common problem in the production of manganese ferroalloys is the lack of knowledge regarding mineralogical and metallurgical properties of manganese ores. Decrepitation, which is described as the breakage or disintegration of the ore particles upon heating, is an important quality parameter of these ores. The decrepitation Index (DI), which is the parameter used to describe the extent of decrepitation, is described as the ratio of mass of particles <6 mm after pre-heating to the total mass of the sample. The purpose of this paper is to describe all the raw data produced during the course of an investigation into the effect of temperature, rotational speed, and particle size on the decrepitation of three types of manganese ores sourced from South Africa. Furthermore, the relevance of the raw data to scientific community as well as industry is explained. The data set will include sub-sets of data i.e. the characterization of the as-received samples, the decrepitation test results, and the characterization of post experiment samples., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2022 The Authors. Published by Elsevier Inc.)

Abstract: A common ferromanganese alloy production problem is the lack of knowledge about the mineralogical and metallurgical properties of the manganese lump ores. An important quality parameter for lump ores is decrepitation, which has not yet been adequately studied. Herein, the physical, chemical and mineralogical characterizations of manganese lump ores from three main Brazilian mines, and from one important South African mine, are presented. After characterization, the samples were separated in three batches: one, as received; the second, after drying at 105°C; and the third, after thermal treatment at 200°C. They were then tested for decrepitation at the temperature of 700°C for 30min, with the particle size range kept between 19 and 6.3mm. The thermal history influence was studied and related to the mineral families present in each ore, i.e., anhydrous-oxide, hydrated-oxide, and silicate–carbonate. A significant difference amongst the decrepitation behaviors was observed for the lump ores from Azul, Urucum, Morro da Mina and Wessel mines. The ores from Wessel (I −6.3mm =12%), Urucum (I −6.3mm=10%) and Azul (I −6.3mm=6%) present a high susceptibility to decrepitation, whilst the silicate–carbonate from Morro da Mina shows no decrepitation. The presence of moisture increased the decrepitation intensity of the Azul, Urucum and Wessel lump ores. The bench-scale heat treatment reduced by more than 60% the decrepitation indexes of Urucum and Azul ores, but was not efficient enough when applied to Wessel ores. [Copyright &y& Elsevier]

Abstract: The primary aims of this study were to determine how vein quartz behaves in an open wood fire and to suggest how burnt quartz may reliably be distinguished from unburnt quartz. Experimental burning was conducted on 10–50 mm pieces of knapped quartz collected from outcrops and beach cobbles near a later Mesolithic and Neolithic quartz scatter at Belderrig, north County Mayo, Ireland. Burning resulted in considerable fragmentation, with the majority of post-burning fragments <10 mm in size. Compared to experiments with flint, few quartz pieces were expelled from the hearth during burning, probably due to lower water content. Burning reduced the lustre and transparency of quartz and oxidized any iron-bearing rock impurities to a red-brown or pink colour, but these changes could only be diagnostic of burning where unburnt quartz of the same type is available for comparison. Burning did not affect the texture of the quartz, though quartz grain boundaries became more visible in some samples. Under the microscope, all >5 μm fluid inclusions in quartz lost their fluid contents, often with the development of fluid escape structures, and this is likely to be a reliable discriminant between burnt and unburnt vein quartz generally, even in the absence of unburnt material for comparison. Burning also creates microfractures, but this feature does not provide a diagnostic test of burning as there is considerable overlap between burnt and unburnt samples in microfracture density. [Copyright &y& Elsevier]

Minute polyphase inclusions in garnet of quartzofeldspathic rocks (saidenbachite) from the Saxonian Erzgebirge, Germany, contain microdiamond or graphite, phlogopite, quartz, paragonite, phengite and other minerals in minor amounts. These inclusions are interpreted to represent an original dense COH + silicate fluid, trapped in crystallizing garnet at depths of >150 km. Inspection of the inclusion population in a single garnet by SEM reveals two characteristic features: (i) The shape of most inclusions indicates healed radial cracks in the host garnet, and, thus, the buildup of a significant differential pressure Δ P, i.e. a contrast in pressure between the inclusion ( Pi) and the host mineral ( Pe). The mineral assemblages sealing the cracks and showing an equilibrated microstructure indicate temperatures of ∼750 ± 50 °C and pressures below 2.5 GPa. (ii) The diverse types of inclusions appear to be randomly distributed in the garnet host. Thus, the variable phase assemblages do not reflect a compositional evolution of the fluid trapped in the garnet. Combining observations (i) and (ii), we propose that the diversity of the phase assemblage in the inclusions is the result of decrepitation at different times, and thus, of distinct histories of Pi, as Δ P at decrepitation is primarily controlled by inclusion size and shape. Applying a flow law for dislocation creep of garnet, a low strength of garnet at 750 ± 50 °C for low geological strain rates is predicted. Thus, differential pressure should have been kept low (i.e. Pi ≈ Pe) by continuous stretching of the inclusion for typical exhumation rates of metamorphic rocks. To attain the differential pressure ( Pi >> Pe) required for catastrophic brittle failure of the garnet host, the decompression rate must have been extremely high. As a robust lower bound, a minimum exhumation rate on the order of 100 m year−1 is suggested, which corresponds to ascent rates of magma. [ABSTRACT FROM AUTHOR]