Bacterial mineralization in weathered pyroclastic deposits of the Kaimondake volcanic ash (4040 ybp) and the Koya pyroclastic flow (6400 ybp) was investigated to evaluate the impacts of bacteria on mineral formation, and to characterize the microbiogenic minerals in the weathering environment. The mineralogy of abiogenic weathering products was also investigated for comparison with the microbiogenic products, and mineral saturation indices were calculated for porewaters using the PHREEQC computer code. The results indicated that these weathered pyroclastic deposits contain 108–109 cells/g, consisting of spherical to rod-shaped bacteria. Associated abiogenic allophane had an Al/Si ratio ranging from 1.01 to 2.13. The bacterial cell surfaces were completely or partially covered by poorly-ordered silicate minerals, which could be divided into two groups based on their chemical and morphological characteristics. Group I was characterized by well developed fibrous to smectite-like flaky habits with variable Al, Si and Fe, corresponding to compositions between proto-imogolite allophane and chamosite. These Al-Si-Fe minerals were the most abundant and major microbiogenic products in both lithologies. Group II exhibited poorly-developed aggregates of allophane-like granular materials composed mainly of Al and Si with minor Fe. Geochemical calculations revealed that the porewaters were saturated with respect to allophane and other crystalline clay minerals such as halloysite, kaolinite, montmorillonite and nontronite. These microbiogenic minerals may be formed as the earliest phase of these clay minerals after interaction of the bacterial cell surfaces with dissolved cations mainly Si, Al and Fe, in the porewaters.

Low-charge beidellites were synthesized by a hydrothermal treatment applied to an amorphous gel phase in basic solution. The hydrothermal conditions for the syntheses were chosen from the stability field of beidellite previously investigated in the literature. The synthetic samples were characterized chemically and structurally using X-ray diffraction, infrared spectroscopy, cation exchange capacity measurement, and chemical and thermal analyses. We compared the synthetic sample with a natural beidellite sample (SbId) from Idaho, USA, looking at chemical composition and particle size. The main difference is the octahedral site occupancy (cis- or trans-vacant layer structure). The natural SbId sample has trans-vacant layers and the synthetic sample has a preferentially cis-vacant character. This character can be modulated, using specific synthesis conditions. The cis- or trans-vacant layer structure of various synthetic beidellites was investigated at low temperature (<350°C) and pressure (<25 MPa). Depending on the pressure and/or synthesis temperature, the proportion of cis-vacant layers ranges from 20 to 100% and increases with the layer-charge deficit.

Starting in 1960, ski resorts in the American West invited American Indian dancers to perform snow dances to address low snowfall. The first documented snow dance was associated with the 1960 Winter Olympics at Lake Tahoe, and snow dances have occurred throughout the twenty-first century, including a 2012 dance at the Vail Ski Resort. In most instances, ski resorts declare the dance successful when snow falls. These snow dances and the related rain dances are best understood in the context of white tourism to the American West and its settler-colonial legacy. I argue that these weather dances are the products of a dynamic relationship between white-owned businesses and American Indian performers in the arid American West, and they have produced racialized ideas of the “sacred”—specifically, an authentic experience that connects settler-colonists to the natural world, facilitated through American Indian spiritual practices. This connection often increases the profitability of businesses that exploit the natural world but also provides an opportunity to express Indigenous communicative agency. I situate the settler-colonial notion of the sacred alongside Indigenous ritual practice, entrepreneurship, and self-determination, using newspapers and anthropological reports.

The mechanism of formation of detrital, beidellite-rich clay occurring in the Agadir basin (Morocco) is well documented, but its detailed characterization is incomplete which limits its application. The aim of the present study was to provide further details of the mineralogical and physico-chemical characteristics of this clay. Bulk raw clay and its Na+-saturated, <2 μm fraction were characterized using chemical, structural, and thermal techniques. Measurements of induced streaming potential (e.g. particle charge) and of specific surface area and porous volume are reported. The raw clay contained carbonate and quartz as associated minerals along with phyllosilicates (<2 μm particle size). X-ray diffraction and scanning electron microscopy analyses showed that the <2 μm fraction was dominated by a dioctahedral smectite. Because dehydroxylation of this mineral occurred at 510°C, and because it re-expanded in ethylene glycol after Li+-saturation followed by heating at 240°C for 24 h, the mineral was shown to be a beidellite rather than montmorillonite. This assertion was further supported by 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra showing predominantly negative charges in the tetrahedral sheets due to notable Al-for-Si substitutions. The chemical composition of the <2 μm fraction showed an Fe2O3 content which was ~7.52 wt.% greater than those of other beidellite occurrences but not so much that it would be identified as a nontronite. The absence of stretching and bending absorption bands corresponding to characteristic (Fe2OH) units in mid-infrared spectra and their corresponding fundamental overtones or combination bands in near-infrared spectra supported this notion. The structural formula of the beidellite in the present study was determined to be (Si7.51Al0.49)(Al2.99Fe0.68Mg0.33) (Ca0.03Na0.54Mg0.11)O20(OH)4, having dioctahedral ferruginous characteristics with almost 60% of the negative charge found in tetrahedral sheets. The cation exchange capacity determined from the structural formula was ~108 meq/100 g. The specific surface area and total pore volume were ~82.2 m2/g and 0.136 cm3/g, respectively. Interestingly, a detrital rather than a hydrothermal-alteration origin, as reported for other beidellite occurrences, explains its natural abundance and emphasizes the great interest in it.

Palygorskite fibers growing along fault planes in the outcrops of a large fault zone in SE Spain (Carboneras Fault Zone: CFZ; Serrata de Níjar) were studied by X-ray diffraction, scanning electron microscopy-energy dispersive X-ray analysis, and transmission electron microscopy-analytical electron microscopy. The structural formulae, calculated per half unit-cell, is: Si7.95Al0.05O20(Al1.93Fe0.08Mg1.92) (OH)2(OH2)4Na0.09K0.01Ca0.034(H2O). The samples have minor tetrahedral substitutions, with Mg/Al ratios close to one, and contain very small amounts of Fe3+. The number of octahedral cations per half unit-cell is 3.93. The fault-hosted palygorskite shows macroscopic ductile features including incipient foliation. Based on field and laboratory observations, as well as on regional geological evidence indicating the existence of widespread hydrothermal processes along the Serrata de Níjar and surrounding areas, we suggest that palygorskite may have formed during ongoing deformation in the CFZ, as a precipitate from Mg-rich hydrothermal fluids.

Illite polytypes are used to elucidate the geological record of formations, such as the timing and provenance of deformations in geological structures and fluids, so the ability to characterize and identify them quantitatively is key. The purpose of the present study was to compare three X-ray powder diffraction (Q-XRPD) methods for illite polytype quantification for practical application to directly date clay-rich fault rocks and constrain the provenance of deformation-related fluids in clay-rich brittle rocks of the upper crust. The methods compared were WILDFIRE© (WF) modeling, End-member Standards Matching (STD), and Rietveld whole-pattern matching (BGMN®). Each technique was applied to a suite of synthetic mixtures of known composition as well as to a sample of natural clay gouge (i.e. the soft material between a vein wall and the solid vein). The analytical uncertainties achieved for these synthetic samples using WF modeling, STD, and Rietveld methods were ±4–5%, ±1%, and ±6%, respectively, with the caveat that the end-member clay mineral used for matching was the same mineral sample used in the test mixture. Various particle size fractions of the gouge were additionally investigated using transmission electron microscopy (TEM) to determine polytypes and laser particle size analysis to determine grain size distributions. The three analytical techniques produced similar 40Ar/39Ar authigenesis ages after unmixing, which indicated that any of the methods can be used to directly date the formation of fault-related authigenic illite. Descriptions were included for pre-calculated WF illite polytype diffractogram libraries, model endmembers were fitted to experimental data using a least-squares algorithm, and mixing spreadsheet programs were used to match end-member natural reference samples.

A review of the models proffered to advance the notion of the metastability of illite shows that these models are not supported by the various data groups that have become available. Given that clay minerals are products of water–rock interactions, low-temperature hydrothermal experiments provide singular insights into their relative stabilities; such experiments with natural materials of contrasting pedigree (illites, sericites, muscovites, and chlorites) show that clay-mineral behaviors in low-temperature hydrothermal solutions are amenable to equilibrium thermodynamic conventions. The data from hydrothermal experiments coupled with data from geothermal fields indicate that muscovite is not a stable phase in the P-T-X range in which authigenic illite occurs; given that experimental data and field occurrence suggest that muscovite and illite have different P-T stability regimes, the continued use of muscovite as a proxy for illite in thermodynamic models is of questionable utility. Furthermore, morphometric studies of clays undergoing illitization show that crystal-size distributions exhibit log-normal patterns. Because log-normal distributions derive from maximum entropy effects, these crystal-size distributions may reflect the effects of entropy production during crystallization rather than kinetically driven Ostwald ripening of illitic phases; the small crystal size of clay minerals may derive from constraints imposed by the physicochemical conditions of their environments of formation. Presumably, irreversible thermodynamics provides the framework for a quantitative understanding of the evolution of complex clay minerals in space and time.

Guanidine and imidazole are important functional molecules that constitute the side chain of basic amino acids (arginine and histidine); these molecules are capable of interacting with mineral surfaces. However, little information is available about the effect of these molecules on mineral dissolution, including amorphous silica. In this study, to evaluate the effect of these organic molecules on the dissolution rates of amorphous silica, dissolution experiments were performed in solutions containing these molecules and other related heterocyclic compounds. The dissolution experiments were conducted by the batch method using 0.1 g of amorphous silica and 100 mL of 0.1 mM NaCl solution with 0.0, 0.1, 1.0, and 10.0 mM of guanidine, imidazole, pyrazole, or pyrrole at pH values of 4, 5, and 6. The results demonstrated that these compounds can enhance the dissolution rate of amorphous silica, depending on their ionic speciation in the following order: guanidine = imidazole > pyrazole > pyrrole. When 10.0 mM solutions were used, both guanidine and imidazole greatly increased the dissolution rate with an enhancement factor of 5.5—6.5, pyrazole exhibited a smaller change in the dissolution rate with an enhancement factor of 1.5—2.4, and pyrrole exhibited no significant enhancement. ChemEQL calculations confirmed that guanidine (pK = 13.6) and imidazole (pK = 6.99) are fully protonated and mostly present as cationic species in a pH range of 4—6; therefore, these compounds are capable of interacting with the >SiO- sites of amorphous silica. Pyrazole (pK= 2.61) and pyrrole (pK = 0.4), however, existed mostly as neutral forms. The concentrations of cationic species of pyrazole and pyrrole were at least one and three orders of magnitude lower than those of fully protonated compounds, respectively; therefore, pyrazole and pyrrole were less reactive than the fully protonated compounds on the surfaces of amorphous silica.

The term ‘montmorillonite’ encompasses a wide range of chemical compositions and structures. Comprehensive and reliable characterization is essential for unambiguous classification. Twenty eight purified, Na-exchanged smectites (<0.2 µm) were characterized by layer-charge measurement using the alkylammonium method, by cation exchange capacity (CEC) measurement with Cu-triethylenetetramine, by determination of the chemical composition using X-ray fluorescence analysis, by calculation of the structural formula following determination of the octahedral structure (trans-vacant vs. cis-vacant) by simultaneous thermal analysis, and by X-ray diffraction analysis. Mössbauer spectroscopy was applied to determine the oxidation state and coordination of Fe and changes thereof during purification of the source materials.

The charge derived from chemical composition was considerably greater (by up to 30%) than the measured layer charge. The independently measured layer charge was used to calculate the structural formula. The measured CEC values, comprising the permanent charges and the pH-dependent edge charges, were consistent with measured layer charge but not with layer charge derived from the chemical composition. Therefore, the structural formula of smectites should be calculated using the measured layer charge.

The dehydroxylation temperature, which conveys information about the structure of the octahedral sheet, was correlated to the amount of Mg and Fe3+ and the location of charges. No relationship was found among the dehydroxylation temperature and the mean layer charge or the Mg content. In contrast, a clear relationship was observed between the Fe content and the dehydroxylation temperature. Montmorillonites with an Fe content <0.3/f.u. are cis-vacant and those containing Fe3+ > 0.3 mol/f.u. are trans-vacant, mostly with additional cis-vacancies. Tetrahedral substitution also appeared to be a function of the number of trans-vacancies.

The parameters analyzed provide the basis for a new descriptive classification system.

Control of the structure and morphology of clay crystals presents a challenge in the synthesis of materials for adsorption and catalysis. In the present study, direct crystallization of a phyllosilicate grafted with organosilyl (methylsilyl and phenylsilyl) groups on the surface of monodisperse spherical silica particles (2.6 μm) is reported. Methyl- and phenyltriethoxysilanes were allowed to react hydrothermally in a Teflon-lined autoclave with silica, MgCl2, and LiF in the presence of urea for 2 or 4 days. X-ray diffraction patterns revealed that the fine platy particles formed were a trioctahedral hectorite-like layered silicate. Greater temperature (150°C) was required to achieve homogeneous coverage of the original spherical silica particles with the hectorite-like particles. The diameter of the initial silica grains increased slightly to 3.0 μm after the hydrothermal reactions, while the original spherical shape and size distribution were maintained. Solid-state 29Si nuclear magnetic resonance analyses confirmed that the presence of resonances attributed to the RSi(OMg)(OSi)2 and RSi(OMg)(OH)(OSi) (R = methyl or phenyl) environments of the silicon proved the formation of covalent bonds between phyllosilicate sheets and the organic moieties. The crystallinity of the layered silicates increased when the reactions ran for a longer time (4 days).

Due to the environmental problems derived from the use of common surfactants as modifiers for clay mineral adsorbents to mitigate mycotoxin contamination of animal feeds, finding non-toxic modifiers to prepare safe and efficient adsorbents is necessary. The objective of the present study was, therefore, to modify acidified palygorskite with polyhexamethylene biguanide (PHMB) to obtain antibacterial polyhexamethylene biguanide/palygorskite (PHMB/Plg) composites for the removal of zearalenone, a common mycotoxin. The PHMB/Plg composites were characterized and analyzed by X-ray diffraction, Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy, and isothermal nitrogen adsorption analysis. The adsorption properties of the composites with respect to zearalenone and their antibacterial activity with respect to Escherichia coli and Staphylococcus aureus were studied. The results indicated that the hydrophobicity of palygorskite was enhanced after modification with PHMB, which could effectively improve the adsorption property of palygorskite toward the nonpolar zearalenone molecules. The adsorption capacity of PHMB/Plg increased with increasing amounts of polyhexamethylene biguanide and increasing pH. The adsorption data were described well by pseudo-second order kinetics and by the Langmuir adsorption model. The maximum adsorption capacity was 2777 μg/g. When the amount of PHMB added increased to 15 wt.%, the composites obtained exhibited good antibacterial performance, and the minimum inhibitory concentrations for Escherichia coli and Staphylococcus aureus were both at 2.5 mg/mL.

The influence of epigenetic (pre-pedogenetic) alteration of basic and ultrabasic rocks leading to the formation of phyllosilicate mineral associations is not well known. The purpose of this study was to gain further understanding of the processes involved by investigating the mineral associations of shallow soils underlain by amphibolites and metamorphosed gabbro-diabases (East Fennoscandia) and by serpentinous dunites (olivinite) and metagabbro amphibolites (the Ural Mountains). Where phyllosilicates were absent from the bedrock, they were also absent from the sola. The pedogenic alteration of the initial mineral soil matrix was very weak and did not result in a significant accumulation of phyllosilicates in the soils (East Fennoscandia). Pedogenesis enhanced the transformation of phyllosilicates, a process initiated by epigenic rock alteration.

Phyllosilicates in the sola from basic and ultrabasic rocks of the Polar Urals were largely inherited according to their origin. The inherited phyllosilicate association of the sola from ultrabasic rocks included talc, serpentine, and chlorite. Saponite resulted from pedogenesis; its distribution in various thin soils dependingon the processes of neoformation and decomposition, the latter probably taking place under the influence of lichens and moss.

Chlorite and illite and products of their transformation, including vermiculite, comprise the phyllosilicate association of a solum from basic rock, and traces of talc were found. The distribution of vermiculite and randomly interstratified chlorite-vermiculite (C-V) depended on the processes of chlorite vermiculitization and vermiculite decomposition.

The formation conditions of the ferric smectite nontronite are not fully understood. The present study couples experimental and analytical data with field observations in an attempt to constrain the rate and temperature of formation of naturally occurring nontronites from Columbia River Basalt flows. Synthetic Fe-Al-Si gels were incubated at temperatures ranging from 4 to 150°C for 4 weeks. Samples were analyzed using Fe K-edge X-ray fluorescence spectroscopy (XAFS). Spectra of the synthesized nontronites were compared with spectra of natural samples collected from weathered Columbia River Basalt flows. Cation ordering in the synthetic samples increased with incubation temperature, but the synthetic clays did not approach the degree of crystal ordering of the natural nontronite samples. These observations suggest that highly ordered natural nontronites require longer crystallization times than are typically used in laboratory experiments. The natural samples were found filling open cracks near flow surfaces, indicating that the clays formed at temperatures below the boiling point of water. A comparison of experimental and field timescales with other estimates of nontronite growth rates suggests that natural nontronite crystallization in the region must have occurred at ambient, near-surface temperatures over timescales of up to millions of years.