Mineralogical Transformations Research Articles

Thermochronology of Alkali Feldspar and Muscovite at T > 150 °C Using the 40Ar/39Ar Method: A Review

The 40Ar/39Ar method applied to K-feldspars and muscovite has been often used to construct continuous thermal history paths between ~150–600 °C, which are usually applied to structural and tectonic questions in many varied geological settings. However, other authors contest the use of 40Ar/39Ar thermochronology because they argue that the assumptions are rarely valid. Here we review and evaluate the key assumptions, which are that (i) 40Ar is dominantly redistributed in K-feldspars and muscovite by thermally-driven volume diffusion, and (ii) laboratory experiments (high temperatures and short time scales) can accurately recover intrinsic diffusion parameters that apply to geological settings (lower temperatures over longer time scales). Studies do not entirely negate the application of diffusion theory to recover thermal histories, although they reveal the paramount importance of first accounting for fluid interaction and secondary reaction products via a detailed textural study of single crystals. Furthermore, an expanding database of experimental evidence shows that laboratory step-heating can induce structural and textural changes, and thus extreme caution must be made when extrapolating laboratory derived rate loss constants to the geological past. We conclude with a set of recommendations that include minimum sample characterisation prior to degassing, an assessment of mineralogical transformations during degassing and the use of in situ dating.

Effect of Mineral Additives on Fusion Behavior of Agricultural Residue Ashes during Combustion or Co-combustion with Lignite

In this work, the ash fusibility behaviour of selected agricultural residues and their blends with lignite was studied, by carrying out chemical, mineralogical, fusibility and thermogravimetric analyses and calculating slagging/fouling indicators for predicting deposition tendencies in boilers. Two additives, bauxite, and clinochlore, were used at varying amounts to reduce ash melting, followed by examining their anti-fusion mechanisms. Initial deformation and softening temperatures of biomass materials were low for combustion processes operating above 900 °C due to their high concentration in K, Na, and P compounds. When the additives were mixed with raw fuels or lignite/biomass blends, the initial deformation of ashes started at temperatures up to 340 °C higher, whereas the fluid temperature in most cases exceeded 1500 °C. Bauxite was more effective than clinochlore. The positive impact of additives was attributed to the mineralogical transformations during ashing to phases with a high melting point through reactions with K, Na-bearing minerals, or CaO of fuel ashes.

Geomagnetic field variations and low success rate of archaeointensity determination experiments for Iron Age sites in Bulgaria

The geomagnetic field variations during the Iron Age (last 1200 years BC) are poorly constrained for Bulgarian territory due to the scarcity of archaeological sites with a well-established chronology. Additionally, the collected Iron Age materials frequently fail to provide reliable archaeointensity data. In an effort to expand the Bulgarian archaeomagnetic database for the last millennia BC and to find an explanation for the low success rate of Thellier experiment, 28 baked clay structures from 10 archaeological sites were archaeomagnetically studied. Magnetically soft minerals dominate in all collections despite the variety of the sampled structures (hearths, domestic ovens, ovens, pottery kilns, burnt dwelling remains, mud-bricks), which suggests differences in the ancient firing conditions. The main carriers are magnetite/titanomagnetite and/or maghemite/titanomaghemite. Verwey transition is well expressed in most samples. Usually more than one magnetic phase exists and noticeable mineralogical transformations occur during laboratory heating. Regardless of all the pre-selection criteria applied, the total success rate of intensity determination is quite low (21%), which seems to be typical for Bulgarian Iron Age materials. At this epoch that starts with a significant decline in the quality of material culture, combustion structures are usually poorly preserved, short-term used (frequently only once) and heated to temperatures around and below 600 °C. A clear relationship is observed between median destructive temperature and success of intensity determination, which suggests that this parameter have a potential as a pre-selection criterion.The new data double the Bulgarian archaeomagnetic dataset for the period in concern with 18 directional and 7 intensity results (6 full vectors). An inclination and intensity decrease is outlined at around 400 BC with assumed variation rates 0.10°/year and 0.32 μT/year, respectively. Considering the whole database, three intensity peaks are detected at circa 1050 BC (Fa ~ 78 μT), 550–500 BC (Fa ~ 96 μT) and 300 BC (Fa ~ 80 μT). The second peak is the highest over the entire eight-millennium long Bulgarian archaeomagnetic record. The first half of the Iron Age (1200–600 BC) is characterized with easterly declinations reaching ~18°E around 1150 BC, while in the last half it turns westerly with westernmost values around 400 BC. The current state of Bulgarian archaeomagnetic reference curves for the Early Iron Age is not sufficient for precise archaeomagnetic dating. Although the resulting dating interval for Ryahovets oven (the only structure with uncertain archaeological dating) coincides with the archaeological evidence, it spans more than 200 years. In such a case, correlation with other archaeomagnetically studied sites from the corresponding period can be especially helpful.

Thermal behaviours of clay mixtures during brick firing: A combined study of in-situ XRD, TGA and thermal dilatometry

The mineralogical transformation of clay material is critical to the firing process for brick manufacturing. In this study, a series of in-situ integrated techniques are used to study the properties of two clay mixtures routinely for production of bricks at a local factory in Queensland, Australia. In-situ XRD, thermal expansion/contraction, thermal weight loss, and microstructural evolution of brick bodies at high temperature have been investigated. Illite/mica persists until 950 °C during the firing process, while K-feldspar transforms into plagioclase with the addition of Ca cations from starting materials. A slower ramp rate decreases the onset temperature of many reactions, including the decomposition of calcite and nucleation/crystallisation of mullite. An increase of firing temperature from 950 to 1150 °C has significantly enhanced the compressive strength of the prepared brick buttons. In addition, six length changing steps have been identified across the temperature range from 30 °C to 950 °C. The contraction of kaolinite between about 420 °C to 850 °C might compensate for the thermal expansion of typical bricks, and may minimise the potential for failure during the α- to β-quartz inversion. However, the rapid shrinkage of metakaolin above 850 °C increases the risk of cracking in manufactured bricks.

Kaolinite-to-Chlorite Conversion from Si,Al-Rich Fluid-Origin Veins/Fe-Rich Carboniferous Shale Interaction

The kaolinite-to-chlorite conversion is one of the chloritization processes that occurs in low temperature diagenetic and hydrothermal systems. The mechanism of this mineralogical transformation is still under discussion, since direct transformation, conversion via berthierine as intermediate phase or direct formation of berthierine/chlorite mix, either by dissolution-crystallization or by solid state transformation (or a combination of both), are all hypotheses put forward. In this context, each description of a kaolinite-to-chlorite conversion occurrence becomes an opportunity to shed new light and to renew this debate. Studying Carboniferous shale–crosscut by large quartz-kaolinite veins–from the mining basin of the North of France, we report therefore an uncommon kaolinite-Fe-rich chlorite assemblage. This assemblage appears as a chlorite fringe 20 µm wide along the interfaces between the shale and the quartz-kaolinite veins. All petrographical, mineralogical and chemical data suggest that the Fe-chlorite results from the interaction between the shale, providing the Fe,Mg supply, and the Si,Al-rich veins, leading to the chloritization of the kaolinite at a small scale via at least one dissolution-recrystallisation step. High-resolution observations highlight that neoformed Fe-rich chlorite contains some 7Å isochemical layers, as relict of berthierine. Therefore, we advance that the conversion takes place either through the precipitation of berthierine following by a second step involving solid state berthierine-chlorite conversion, or through the direct precipitation of a chlorite-rich/berthierine-poor mix driven by the Fe/(Fe + Mg) ratio, at low temperature and in reducing conditions. The comparison of our data with the recent literature allows to prefer the second hypothesis.

Metal(loid)s remobilization and mineralogical transformations in smelter-polluted savanna soils under simulated wildfire conditions

The surroundings of mines and smelters may be exposed to wildfires, especially in semi-arid areas. The temperature-dependent releases of metal(loid)s (As, Cd, Cu, Pb, Zn) from biomass-rich savanna soils collected near a Cu smelter in Namibia have been studied under simulated wildfire conditions. Laboratory single-step combustion experiments (250–850 °C) and experiments with a continuous temperature increase (25–750 °C) were coupled with mineralogical investigations of the soils, ashes, and aerosols. Metals (Cd, Cu, Pb, Zn) were released at >550–600 °C, mostly at the highest temperatures, where complex aerosol particles, predominantly composed of slag-like aggregates, formed. In contrast, As exhibited several emission peaks at ~275 °C, ~370–410 °C, and ~580 °C, reflecting its complex speciation in the solid phase and indicating its remobilization, even during wildfires with moderate soil heating. At <500 °C, As was successively released via the transformation of As-bearing hydrous ferric oxides, arsenolite (As2O3) grains attached to the organic matter fragments, metal arsenates, and/or As-bearing apatite, followed by the thermal decomposition of enargite (Cu3AsS4) at >500 °C. The results indicate that the active and abandoned mining and smelting sites, especially those highly enriched in As, should be protected against wildfires, which can be responsible for substantial As re-emissions.

Мінералогічні особливості відновлених окатишів Північного гірничозбагачувального комбінату (Криворізький басейн)

The advantages of reduced iron ore pellets over oxidized ones have been considered. The chemical and physical parameters of the primary material have been given: iron ore (magnetite) concentrate (iron content is 67.30 mass %; particle size distribution is 97.0 % of 0.056 mm fraction), bentonite (montmorilonit content is 70.43 mass %; particle size distribution is 94.5% of 0.056 mm fraction), ground coke. The course of experiments has been described. The zonal structure of the obtained pellets has been characterized: the central zone is composed of hematite with relics of magnetite; intermediate one contains magnetite particles with inclusions of hematite; peripheral zone includes subidiomorphic crystals of magnetite and their dendritic aggregates. The bentonite component in the central and intermediate zones retained a crypto-crystalline structure, in the peripheral one it had been transformed into a crystalline aggregate of garnet and pyroxene. Emphasis is placed on the need to verify the impact of various indicators of temperature, firing time, quantitative ratios of charge components, mineral and chemical composition of the cementing material on mineralogical transformations.

Improvement of engineering properties of expansive soil using liming leather waste ash

The expansive soils have always presented various challenges for geotechnical and civil engineers due to their low bearing capacity and high swell-shrinkage characteristics. This study aims to utilize liming leather waste ash (LLWA) as a sole expansive soil stabilizer examining its effects on various engineering properties of soil such as consistency limits, compaction parameters, unconfined compressive strength (UCS), California bearing ratio (CBR), and swell parameters. The observations are also made on the curing effects on the strength parameters of the soil-additive mix. It was observed that the LLWA contains cementitious characteristics of lime and silica combined and can substantially reduce the plasticity and swell-shrink behavior of the soil and improve its strength and bearing characteristics. The UCS and CBR values have also shown multifold increase post curing with UCS and soaked CBR escalating by 278% and 387% respectively. The test results are further explained through the microstructure study which confirms the mineralogical transformation and cementation of soil particles. A one-dimensional rainfall-simulated leachate study has been carried out over a pavement model at the end to access the possible impact of ash treatment on the water table.

LITHOGENESIS OF TERRIGENOUS ROCKS AND ITS INFLUENCE ON FILTRATION-CAPACITY PROPERTIES OF LOWER CARBON RESERVOIRS IN THE CENTRAL PART OF THE DNIEPER-DONETS BASIN

On the basis of lithological and petrographic studies of core material from 28 wells in the Sribnenskoy depression (central part of the Dnieper-Donetsk depression) lithogenetic transformations have been shown that occur in glibokosanuren (more than 5000 m) sandstones of the Lower Carboniferous. By the nature of structural and mineralogical transformations, secondary (post-sedimentation) processes of lithogenesis of terrigenous rocks-hydrocarbon reservoirs have been established and their influence on reservoir properties has been revealed.

Characterization, thermal behaviour and firing properties of clay materials from Cap Bon Basin, north-east Tunisia, for ceramic applications

AbstractThis study focuses on the characterization, thermal behaviour and firing properties of clays from Cap Bon Basin, Tunisia. Chemical (inductively coupled plasma atomic emission spectroscopy) and mineralogical (X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy) characterization of the clays was carried out. Physical properties were identified using particle-size distribution and Atterberg limits tests. Differential thermal analysis/thermogravimetry, dilatometry, XRD and FTIR analyses were conducted to assess the thermal behaviour, transformations and crystalline phase development during firing. The clays studied show large proportions of silt and clay fractions. They are rich in SiO2, Al2O3 and Fe2O3 and mostly consist of illite, kaolinite, smectite and minor mixed-layer illite-smectite. Associated minerals are mainly quartz, calcite and feldspar. To monitor the firing properties, three clay mixtures referred to as M1, M2 and M3 were prepared according to the physicochemical and mineralogical characteristics of the raw clays. These were sintered at 900°C, 1000°C and 1100°C and tested for firing shrinkage, flexural strength and water absorption. As a result, various mineralogical transformations occurred at 900–1100°C associated with the crystallization of new phases. The main transformations identified at &gt;1000°C resulted in the formation of anorthite and mullite, causing significant densification of the fired ceramic materials. Sintering at 1100°C increased the densification and thus improved the flexural strength. At this temperature, the sintered ceramic tiles exhibited excellent properties, namely water absorption of 2–3% and flexural strength of 30–41 MPa, indicating that these studied clays might be used as raw materials for the production of stoneware tile ceramics.

Element enrichment/depletion during faulting in shale-rich surface exposures of the 2008 Wenchuan earthquake (Mw 7.9) and implications for coseismic temperature

The coseismic frictional temperature is increasingly recognised as an important factor for the transformation mechanism in shallow crustal faulting. We report changes in the mineralogical and geochemical compositions across the fault zone in the Shaba (SB) exposure of the 2008 Wenchuan earthquake (Mw 7.9), which contained the maximum value of vertical displacement and cut through shale-rich strata by the principal slip surface. Assuming Yb to be an immobile trace element, with respect to those in the adjacent damaged zone and wall rocks, Li, Rb, Cs and most light rare earth elements (LREE) exhibited marked enrichments of 143%, 247%, 475% and >60%, respectively; and a 40% depletion of Sr and <5% depletion of most heavy rare earth elements (HREE) was found, responding to mineralogical transformation such as alteration and dissolution of feldspar and formation of abundant clay minerals. In addition, heterogeneous adsorption of clay minerals could result in fractionation between and within LREE and HREE as well as negative Eu anomalies and positive Ce anomalies. The element enrichment/depletion model of the northern segment of the Yingxiu–Beichuan (YX–BC) fault zone was quite different from the middle/southern segments characterising faults in carbonate and granitic rocks. Through model calculation, the calculated trace element compositions (Li, Rb, Sr, Cs, Ba, La, Sm and Pb) of the fault gouge were obtained at 250 °C, 300 °C and 350 °C, and were produced by frictional heating. By comparing with the observed values, we suggest that high temperatures derived from frictional heating or due to buffering of the slip zone temperature by evaporation of pore water during the earthquake within the principal slip surface in the northern segment of the YX–BC fault zone may not have existed. Mechanical crushing and chemical alteration (not under high-temperature conditions) within the fault zone during the coseismic stage may result in mass removal and element enrichment/depletion. KEY POINTS Mineralogical and geochemical compositions were reported in the Shaba exposure of the 2008 Wenchuan earthquake. Li, Rb, Cs and most LREE exhibited marked enrichments in the fault gouge. Fractionation between and within LREE and HREE, negative Eu anomalies and positive Ce anomalies occur in the fault gouge. High temperatures may not have existed within the principal slip surface of the northern segment of the YX–BC fault zone.

Integration of diagenesis in basin-scale, stratigraphic forward models using reactive transport modeling: Input and scaling issues

This article presents an integrated approach based on stratigraphic forward modeling and reactive transport modeling to adequately represent the development of a mixed siliciclastic-carbonate sedimentary system and its diagenesis. This work was realized on a realistic case study, the Oligo-Miocene series of Carry-le-Rouet, South-East of France, characterized by a complex pattern of bioclastic, bioconstructed and siliciclastic deposits, and affected by several exposure surfaces and associated meteoric diagenesis. A first phase consisted in building a stratigraphic forward model (SFM), using the software DionisosFlow. The construction of the model was based on sensitivity tests on the two main parameters controlling basin sedimentation: 1) competition between carbonate production and siliciclastic supply; 2) subsidence. The results of the simulations, especially the facies distribution, the thickness of the deposits and the sedimentary architectures were compared with the observed data to validate the model. A second phase consisted in focusing on a specific stratigraphic event and performing reactive transport modeling (RTM) on a 2D section extracted from the DionisosFlow model to evaluate the mineralogical transformations and resulting petrophysical evolutions created by early diagenesis. The calculation results show the occurrence of two domains of salinity, that were associated with two distinct diagenetic environments: marine and meteoric phreatic. Globally, the simulated diagenetic trends are qualitatively consistent with the petrographic observations, except for the replacement of aragonite by a calcite cement, that systematically occurred in the model and is not always observed in thin sections. This preliminary study emphasizes the issues associated with the application of RTM to diagenetic phenomena, linked with the uncertainties inherent to specific parameters, such as minerals kinetic properties, and the mismatch between the space and time scales of the modeled processes and the upscaled description of each SFM cell. These results argue in favor of an alternative solution, that could conciliate the different processes. The combination of the various SFM output properties with simplified chemical reactions whose rates have been tuned for specific diagenetic processes of interest could provide diagenetic risk maps that would constitute useful guides for exploration at basin scale.

The mineralogical and lithogeochemical footprint of the George Fisher Zn-Pb-Ag massive sulphide deposit in the Proterozoic Urquhart Shale Formation, Queensland, Australia

The Proterozoic Carpentaria Province (McArthur basin and Mount Isa Inlier) in northern Australia comprises a number of world class clastic dominated (CD-type) Zn-Pb massive sulphide deposits, formally known as SEDEX deposits. In order to identify the geochemical footprint of any mineralizing system it is necessary to characterize compositional variability of the host rock to mineralization. In the southern Carpentaria, establishing the baseline composition of the host rock is complicated by varying degrees of tectonic overprint, a lack of metamorphic indicator minerals, and the overall size of the ore forming systems. In this study, samples from drill-holes intersecting the main ore bodies at the world class George Fisher CD-type massive sulphide deposit have been compared to samples from a drill-hole intersecting barren, correlative lithologies of the Urquhart Shale Formation (ca. 1654 Ma). Bulk rock lithogeochemical (X-ray fluorescence, inductively coupled plasma mass spectrometry and LECO) and mineralogical (X-ray diffraction) analyses have been combined with petrographic observations to (1) establish the baseline composition of the Urquhart Shale Formation and (2) determine the geochemical and mineralogical footprint of the CD-type system at George Fisher. The absence of metamorphic indicator minerals, combined with the preservation of illite in un-mineralized Urquhart Shale, suggests that in this part of the Mount Isa area, the host rocks did not reach greenschist facies conditions (>300 °C). Chlorite in the un-mineralized Urquhart Shale is very fine grained (≤ 10 μm) within interstitial pore spaces with other phyllosilicates (e.g., illite), and is interpreted to be diagenetic in origin. Relative to the un-mineralized Urquhart Shale, the first stage of sulphide mineralization (Zn-dominated, stratabound) at George Fisher is associated with decreased abundances of albite, chlorite, and calcite, and higher abundances of dolomite and phyllosilicates (muscovite and phlogopite). These mineralogical transformations are associated with strong minor and trace element depletion (Sr and Na) and enrichment (Tl and Mn). An element index based on this suite of elements (GF index = 10400Tl+Mn10Sr+Na) is highly effective in differentiating between the background Urquhart Shale Formation and the alteration footprint at George Fisher and may provide an additional tool for geochemical exploration programmes in the Mount Isa area. This study affirms the benefit of combining lithogeochemical, mineralogical, and petrographic data in order to understand the host rock baseline composition and the alteration footprint of Carpentaria CD-type massive sulphide systems.

Evaluating the Impact of Organic Addition and Aggregate Gradation on Air Lime Mortar: New Compatible Green Material for Heritage Application

ABSTRACT This research aims to study the influence of organic additive and aggregate grain size in lime mortar hardening for producing compatible, high-performance and eco-friendly materials for conservation and restoration of heritage structures. Mortar mix with lime to sand ratio of 1:3 by mass and water to binder ratio of 0.75 was considered. Ficus Carica (Moraceae), commonly known as Fig fruit, was used as an organic additive in the mortar mix at 2, 4 and 6% in volume. River sand grounded for 5, 10 and 15 minutes, turning in changes in grain-size distrubution, was used in the mortar mix. Investigations on mortars were performed after 90 curing days; physical and mechanical properties were evaluated, along with mineralogical changes due to organic addition; the influence of organic and aggregate grading in carbonation rate was also assessed. Results indicate that the aggregate with retention value 45 ± 3% in grades between 2 mm to 425 micron and 425 micron to 75 micron; and the addition of organic additive at 4% in volume represents the optimum mix able to assure significant enhansement in carbonation rate and mechanical resistance. Polysaccharides in organic played the central role in the mineralogical transformation responsible for the measured enhanced performances.

Out of the oven and into the fire: Unexpected preservation of the seasonal δ18O cycle following heating experiments on shell carbonate

Oxygen isotope values of shell carbonate sampled along the growth trajectory of fossil mollusks provide one of the few types of proxy data available for reconstructing seasonal temperature variation in Earth's past. Understanding how diagenesis affects the preservation of seasonal cycles is key to their interpretation in a paleoclimate context. An assumption common in the literature, albeit tenuous, is that the alteration of an aragonite shell to calcite will homogenize intra-shell stable isotope variation, thus attenuating or erasing any seasonal cycle and resetting bulk shell values. Demonstration of regular variation in δ18O values across growth bands in a still-aragonite mollusk is therefore generally interpreted to reflect retention of the primary environmental signal. However, this implied assumption remains untested, and experimental studies have demonstrated that heating can decrease shell δ18O values with negligible mineralogical transformation. Here we investigate how dry heat impacts both the geochemistry and mineralogy of shell aragonite by roasting time-equivalent shell sections of a modern bivalve, Spisula solidissima, at 200 °C for intervals ranging from 2 hours to 2 weeks, and comparing seasonal oxygen isotope variations recovered from the same one-year period of shell accretion with those from untreated shell. Oxygen isotope values from heated shell sections decline by as much as 1.5‰ across all parts of the ~2.5‰ annual cycle, and degree of 18O depletion decreases logarithmically with time heated. Neither Raman spectroscopy nor X-ray diffraction indicate mineralogic change in association with heating. Scanning electron microscopy reveals that heating results in some intra-crystal pitting and subtle smoothing of crystal edges, but heated shell lacks any textural evidence for inversion to calcite, suggesting that fine-scale isotopic exchange may take place with shell-bound water vapor and/or organic matter. The surprising magnitude of this shift in the absence of mineralogic transformation highlights the potential impact of diagenetic processes on the preservation of paleotemperature signals, seasonal or otherwise, in accretionary biogenic carbonates, and suggests a need for more stringent guidelines in assessing the preservation of these materials during the employment of common sclerochronological methodologies.

Silicon and Aluminum Mobility in Soils of Jeju Island, Korea

The objective of the study is to investigate the effect of released silicon (Si) and aluminum (Al) during the formation of volcanic ash soil on the content of Si in groundwater on Jeju Island. Volcanic ash soils in Jeju Island were formed from pyroclastic materials that originated from basalt. We sampled four profiles, including basaltic bedrock of each soil series with large variations in elevation (160–320 m) and mean annual precipitation (MAP; 1,800–2,600 mm). The soil and bedrock minerals were analyzed for weathering of volcanic ash soils related to mineralogical transformations and mobility of Si and Al. Andisols (above 2,000 mm MAP) were dominantly composed of allophane and gibbsite. In Andisols used in the study, 10–70% of Si was lost, whereas the amount of Al was relatively conserved. This is because Al forms Al-humus complex and Andisols contain allophane. In contrast, non-Andisols located at low altitude with lower than 1,800 mm MAP were enriched with considerable amounts of Si and Al, because non-Andisols have crystalline clay minerals and quartz. These results indicate that Andisols, which are widely distributed in Jeju Island, may play an important role in contributing to the high concentration of dissolved Si in the groundwater.

Reductive transformation of birnessite and the mobility of co-associated antimony

Manganese (Mn) oxide minerals, such as birnessite, are thought to play an important role in affecting the mobility and fate of antimony (Sb) in the environment. In this study, we investigate Sb partitioning and speciation during anoxic incubation of Sb(V)-coprecipitated birnessite in the presence and absence of Mn(II)aq at pH 5.5 and 7.5. Antimony K-edge XANES spectroscopy revealed that Sb(V) persisted as the only solid-phase Sb species for all experimental treatments. Manganese K-edge EXAFS and XRD results showed that, in the absence of Mn(II), the Sb(V)-bearing birnessite underwent no detectable mineralogical transformation during 7 days. In contrast, the addition of 10 mM Mn(II) at pH 7.5 induced relatively rapid (within 24 h) transformation of birnessite to manganite (~93%) and hausmannite (~7%). Importantly, no detectable Sb was measured in the aqueous phase for this treatment (compared with up to ∼90 μmol L−1 Sb in the corresponding Mn(II)-free treatment). At pH 5.5 , birnessite reacted with 10 mM Mn(II)aq displayed no detectable mineralogical transformation, yet had substantially increased Sb retention in the solid phase, relative to the corresponding Mn(II)-free treatment. These findings suggest that the Mn(II)-induced transformation and recrystallization of birnessite can exert an important control on the mobility of co-associated Sb.

Lichens Bite the Dust - A Bioweathering Scenario in the Atacama Desert.

SummaryBioweathering mediated by microorganisms plays a significant role in biogeochemical cycles on global scales over geological timescales. Single processes induced by specific taxa have been described but could rarely be demonstrated for complex communities that dominate whole landscapes. The recently discovered grit crust of the coastal Atacama Desert, which is a transitional community between a cryptogamic ground cover and a rock-bound lithic assemblage, offers the unique chance to elucidate various bioweathering processes that occur simultaneously. Here, we present a bioweathering scenario of this biocenosis including processes such as penetration of the lithomatrix, microbial responses to wet-dry cycles, alkalinolysis, enzyme activity, and mineral re-localization. Frequently occurring fog, for example, led to a volume increase of microorganisms and the lithomatrix. This, together with pH shifts and dust accumulation, consequently results in biophysical breakdown and the formation of a terrestrial protopedon, an initial stage of pedogenesis fueled by the grit crust.

Archaeometry of fire aided limnosilicite mining in the Avas-Tűzköves (Miskolc, NE-Hungary) Paleolithic silica source

ABSTRACT This paper communicates new results on fire aided limnosilicte mining in a Hungarian paleolithic site. The beneficial effect of temperature on material fragmentation and chipping was proved by laboratory experiments, with samples fired at 260°C and 360°C. Mineralogical transformations which lead to fragmentation are triggered by heating and were characterized by analytical methods in detail. The raw material is nanocrystalline quartz dominant silicolite with amorphous silica, moganite and traces of goethite and tridymite, identical to length-fast chalcedony. X-ray diffraction revealed the recrystallization of amorphous silica into quartz, accompanied by H2O loss measured by thermogravimetry. Using attenuated total reflectance Fourier-transformed infrared spectroscopy, both H2O and OH content, their loss by heating and recrystallization was evidenced. Scanning electron microscopy on chipped surfaces revealed the disappearance of the fibrous texture, promoting the knappability of the material. The main factors influencing fire-aided mining and/or processing were identified as H2O pressure, amorphous silica crystallization as a result of H2O and OH removal from the silanol groups and change in quartz crystallite morphology.

A comparative study of typical early celadon shards from Eastern Zhou and Eastern Han dynasty (China)

Many Chinese scholars thought that the development of celadon could be divided into two stages, proto and mature. The two types of wares were considered to have significant differences in product quality. In recent years, people have many controversies about the celadon classification, because many proto shards with high quality from Eastern Zhou dynasty (770–221 BCE) were unearthed. In this paper, we collected these typical proto celadon shards and some early mature wares from Eastern Han Dynasty (24–220 CE), and compared them in terms of body, glaze and firing. Based on analysis results, we believe that both types of potshards used porcelain-stone as the raw material and were applied lime-rich glaze. Most of them have relatively high firing temperature (above 1000 °C) and completed mineralogical transformation in their fired bodies. The differences between them are mainly glazes’ appearance and thickness uniformity, content of minerals (especially cristobalite) contained in the bodies and control of firing process. These conclusions should be useful for the further discussion about the celadon classification.