Supra-glacial material, including light-absorbing impurities (LAI) such as mineral dust of crustal and soil origin, black carbon, algae and cryoconite, reduce the reflectance of snow and glacier ice. ...The reduction depends on the amount of LAI and their physical and chemical properties, which vary spatially and temporally. Spectral reflectance data and snow and ice samples, containing LAI, were collected in the ablation zone of the Djankuat Glacier, Central Caucasus, Russia. The spectra of the samples containing mineral dust transported from deserts were characterized by negative visible near-infrared gradients and were different from the spectra of clean aged snow and exposed glacier ice and from the samples containing mineral dust produced locally. Geochemical and mineralogical analysis using X-ray diffraction and X-ray fluorescence spectrometry showed that samples containing desert dust were characterised by a high proportion of clay materials and such minerals as smectites, illite–smectites and palygorskite and by a smaller size of mineral particles. They were enriched in chromium, zinc and vanadium. The latter served as an indicator of dust transport over or origin from the oil-producing regions of the Middle East. There was a strong negative correlation between the amount of organic matter and mineral dust in the collected samples and the albedo of surfaces from which the samples were collected. The results suggested that organic matter reduced albedo more efficiently than mineral dust. The study highlighted the importance of supra-glacial material in changing the surface reflectivity of snow and glaciers in the Caucasus region.
•The value of ΔfHmo(T=298.15K) of Al-rich palygorskite was determined by melt solution calorimetry.•The thermodynamic properties of Mg-rich and (Al+Mg) palygorskites were calculated.•The enthalpies ...of removal of different types of water in palygorskite were measured.
This paper presents the results of the first experimental thermochemical study of the Al-rich palygorskite (Al2Mg2)Si8O20(OH)2(H2O)4·5H2O (Crimea, Ukraine) made with the help of a high-temperature heat-flux Tian–Calvet microcalorimeter. The natural palygorskite was characterized by scanning electron microscopy, X-ray fluorescence analysis, X-ray powder diffraction, thermal analysis, FTIR spectroscopy. The standard molar enthalpies of formation from the elements were determined by the melt solution calorimetry for palygorskite with various content of different types of water in accordance with Hess’s law. The values of the standard enthalpies of formation at T=298.15K were found to be −(12,560±36)kJ·mol−1 for (Mg2Al2)Si8O20(OH)2(H2O)4·3.5H2O; −(11,535±26)kJ·mol−1 for (Mg2Al2)Si8O20(OH)2(H2O)4 and −(10,353±16)kJ·mol−1 for (Mg2Al2)Si8O20(OH)2. On the basis of experimental data for natural Al-rich palygorskite the thermodynamic properties of Mg-rich palygorskite and palygorskite with intermediate (Al+Mg) composition were calculated. The enthalpies of removal of different types of water were measured. It was found that the value of enthalpy of removal of adsorbed and zeolitic water was significantly lower than the enthalpy of removal of the coordinated water, it corresponds to the greater bond strength of coordinated water than adsorbed and zeolitic water in the structure of layered minerals of (palygorskite+sepiolite) group.
•Glucose addition stimulated microbial activity in soils.•In sands, friction angle decreased while cohesion increased; in loams, compressive strength decreased.•Illite layers in mixed layer clay ...minerals were turned into smectite.•Microbial cells and EPS enmeshed solid particles.•With decreasing microbial activity, stress-strain properties partly recovered.
High inputs of easily available organic matter to the subsurface may quickly activate the native microbial communities, thereby changing soil engineering properties. We studied the effect of glucose addition, an easily available carbon source, on stress-strain properties, mineralogy, and microstructure of several loamy and sandy soils over 30 days in laboratory experiments. During the period of high microbial activity, direct shear tests revealed a reduction of the friction angle of 15–30 % and a raise of cohesion in sands. Unconfined compression tests showed a 20–30 % decrease in the compressive strength of loamy soils. With the decline of microbial activity, the stress-strain properties recovered partially. The alterations of the stress-strain properties with increasing microbial activity were linked to changes in mineralogy and composition. X-ray diffraction showed that the proportion of smectite layers in illite-smectite mixed layer minerals increased, as well as the overall imperfection of clay minerals. Glucose addition resulted in a temporary increase in the content of microaggregates (0.1-0.05 mm). Newly formed linkages of organic matter between solid particles, biofilm formation and direct interaction of cells with mineral surfaces were observed by scanning electron microscopy. Our data show that microbial-mediated processes may adversely influence stress-strain properties of soils and endanger the safety of buildings.
During the Arctic Coring Expedition (ACEX), a 428‐m‐thick sequence of Upper Cretaceous to Quaternary sediments was penetrated. The mineralogical composition of the upper 300 m of this sequence is ...presented here for the first time. Heavy and clay mineral associations indicate a major and consistent shift in provenance, from the Barents‐Kara–western Laptev Sea region, characterized by presence of common clinopyroxene, to the eastern Laptev‐East Siberian seas in the upper part of the section, characterized by common hornblende (amphibole). Sea ice originating from the latter source region must have survived at least one summer melt cycle in order to reach the ACEX drill site, if considering modern sea ice trajectories and velocities. This shift in mineral assemblages probably represents the onset of a perennial sea ice cover in the Arctic Ocean, which occurred at about 13 Ma, thus suggesting a coeval freeze in the Arctic and Antarctic regions.
The article is dedicated to the study of mineral composition and genesis of Desiatiy Khutor deposit of bentonite clays located in the Republic of Khakasia. The mineral composition of natural samples ...and fraction < 0.5 mm was studied in details by X-ray diffraction. On the basis of the geological structure,tectonic and mineragenous zoning data, the deposit was designated to a particular genetic type of deposits, lying among coal-bearing rocks. Promising areas for bentonite exploration were highlighted within this bentonite- bearing province.
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