Crystal-chemistry of micas belonging to the yangzhumingite-fluorophlogopite and phlogopite-fluorophlogopite series from the Apuan Alps (northern Tuscany, Italy)

The present work reports the crystal-chemical characterization of micas from the Monte Arsiccio and Buca della Vena mines (Apuan Alps, Italy) through electron microprobe analysis, single-crystal X-ray diffraction, and Raman spectroscopy. The sample from the Monte Arsiccio mine can be classified as an intermediate member of the yangzhumingite-fluorophlogopite series, with average crystal-chemical formula (K0.85Na0.01Ba0.09)Σ=0.95(Mg2.11Fe2+0.23Fe3+0.11Cr3+0.01Al0.20Ti0.04☐0.30)Σ=3.00(Si3.20Al0.80)Σ=4.00O10.00F1.90Cl0.02(OH)0.08. Unit-cell parameters are a ~ 5.30, b ~ 9.18, c ~ 10.14 Å, β ~ 100.12°, V ~ 486.22 Å3, corresponding to the 1M polytype. Structure refinements, performed in C2/m space group, converged to R1 = 3.54 and 4.46% and provided Mg plus Fe occupancy in the range 86–94% for the octahedral M1 and M2 sites. Raman spectroscopy shows very weak bands in the OH stretching region at ~ 3690 and 3580 cm−1. The sample from the Buca della Vena mine has been identified as an (OH)-rich fluorophlogopite, with average crystal-chemical formula (K0.84Na0.02Ca0.01)Σ=0.87(Mg2.12Fe2+0.55Fe3+0.10Al0.18☐0.05)Σ=3.00(Si2.99Al1.01)Σ=4.00O10.00F1.02Cl0.09(OH)0.89. Its unit-cell parameters are a ~ 5.33, b ~ 9.22, c ~ 10.23 Å, β ~ 100.09°, V ~ 494.39 Å3. Structure refinements gave good R1 values (3.27 and 4.37%) and revealed octahedral occupancy of 82–84% Mg and 16–18% Fe. Strong Raman signals at ~ 3702 cm−1 and 3595 cm−1 were observed in the OH stretching region. The findings allow to better understand not only the mineralogy of the Apuan Alps but, more generally, the crystal chemical details of intermediate dioctahedral-trioctahedral mica belonging to the yanzhumingite-fluorophlogopite series.

Vanadium occupation and its leachability differences in trioctahedral and dioctahedral mica

Vanadium in black shale prefers to locate in the octahedron of mica and can be more easily released from trioctahedral mica than dioctahedral mica.

Microbial Lithotrophic Oxidation of Structural Fe(II) in Biotite

ABSTRACTMicroorganisms are known to participate in the weathering of primary phyllosilicate minerals through the production of organic ligands and acids and through the uptake of products of weathering. Here we show that the lithotrophic Fe(II)-oxidizing, nitrate-reducing enrichment culture described by Straub et al. (K. L. Straub, M. Benz, B. Schink, and F. Widdel, Appl. Environ. Microbiol. 62:1458–1460, 1996) can grow via oxidation of structural Fe(II) in biotite, a Fe(II)-rich trioctahedral mica found in granitic rocks. Oxidation of silt/clay-sized biotite particles was detected by a decrease in extractable Fe(II) content and simultaneous nitrate reduction. Mössbauer spectroscopy confirmed structural Fe(II) oxidation. Approximately 1.5 × 107cells were produced per μmol of Fe(II) oxidized, in agreement with previous estimates of the growth yield of lithoautotrophic circumneutral-pH Fe(II)-oxidizing bacteria. Microbial oxidation of structural Fe(II) resulted in biotite alterations similar to those found in nature, including a decrease in the unit cell b dimension toward dioctahedral levels and Fe and K release. Structural Fe(II) oxidation may involve either direct enzymatic oxidation, followed by solid-state mineral transformation, or indirect oxidation as a result of the formation of aqueous Fe, followed by electron transfer from Fe(II) in the mineral to Fe(III) in solution. Although it is not possible to distinguish between these two mechanisms with available data, the complete absence of aqueous Fe in oxidation experiments favors the former alternative. The demonstration of microbial oxidation of structural Fe(II) suggests that microorganisms are directly responsible for the initial step in the weathering of biotite in granitic aquifers and the plant rhizosphere.

Another insight into illitization by K-Ar dating of micro- to nano-metric illite-type particles exchanged with alkylammonium cations

Micrometric and nanometric illite-rich size fractions of claystones, bentonites and shales were exchanged with alkylammonium cations that have the specificity of stoichiometrically replacing K in trioctahedral mica interlayers. The purpose of the study was a separate evaluation of the K-Ar ages of potentially dioctahedral residual particles not affected by alkylammonium leaching and of potentially trioctahedral illites that were exchanged by the organic molecules.The K-Ar ages of micrometric size fractions from an Estonian Blue Clay sample collected next to another studied previously show that, even if identical in their mineralogical characteristics, the fractions contain variable amounts of trioctahedral particles that are of different origins. The alkylammonium treatment modifies slightly, within analytical uncertainty, the K-Ar ages of the <0.1 and 0.1–0.4 mm size fractions from, respectively, 464±13 and 530±14 Ma before organic exchange to 480 ± 11 and 546±12 Ma after. The K-Ar ages of alkylammonium exchanged nanometric size fractions from the rim and centre of a thick Upper Cretaceous bentonite bed in Montana suggest that trioctahedral illite-rich particles mineralogically and chemically homogeneous and about 30 Ma old precipitated next to older dioctahedral particles of ∼60–65 Ma. The untreated mixtures consist of two generations of authigenic illite having apparently different di/trioctahedral layerings. The same type of authigenic di/trioctahedral illite layering could be demonstrated for nanometric illite particles of a bentonite bed from the East Slovak Basin, one size fraction appearing to even consist of a pure trioctahedral illite as the alkylammonium exchange emptied completely the illite interlayers. The nearby shale level consisted of detrital illite particles that were found to be of different ages, di/trioctahedral layerings and therefore varied origin.K-Ar ages of alkylammonium exchanged micrometric to nanometric illite and illite-smectite mixed layers, either increasing or decreasing, appear to outline variable di/trioctahedral layering assemblages or independent particle mixtures resulting from a more complex smectite illitization process than the conventionally assumed homogeneous reaction. It could record changing chemical compositions of the interacting pore fluid during crystallization, even when illitization progressed slowly. Similar ages before and after alkylammonium exchange suggest a constant chemical composition and therefore an homogeneous dioctahedral crystal structure. Alternatively, a changing chemical composition of the fluids during illitization is potentially recorded by variable K-Ar ages of the alkylammonium-leached illite resulting from differentiated ion exchanges.

MINERALOGICAL COMPOSITION AND SOIL MICROSTRUCTURE OF THE ACCUMULATIVE-DENUDATION LANDSCAPE OF THE NORTHERN PART OF THE FOREST STEPPE AND IN CASE OF MATERIAL EROSION

The distribution of clay minerals of the fraction less than 1 micron, extracted from typical, alkaline, podzolized agronomic black earths, depends on the type of soil, lithology of soil-forming rocks and relief. The silt fraction of agrochernozems developed on the quaternary loess-like heavy loam consists of smectite phase, represented by complex disordered mica-smectite formations, di-trioctahedral mica, kaolinite, chlorite. Agroblack soils formed on sediments in which include Neogene eluvium, contain a smectite phase represented by montmorillonite itself and badelyte with clinoptylolites in it. Erosion-resistant the material is represented by rounded aggregates, the structure of which was determined by micromorphological analysis. In the composition of micaceous micaceous fraction, extracted from this material, is dominated by micaceous mectritic formation. The conclusion is made about the demolition of the most valuable fertility of aggregated material - product of interaction smectite phase with organic matter.

Magnetic behaviour of trioctahedral mica-2M1 occurring in a magnetic anomaly zone

This work relates the crystal chemistry and the magnetic behaviour of a trioctahedral mica (chemical formula: (K0.90Na0.01Ca0.01Ba0.01 ☐0.07)(Al0.05Fe2+1.10Mg1.38Ti0.32Mn0.01☐0.04)(Al1.12Si2.88)O10 (F0.27OH1.27O0.46); unit cell parameters: a = 5.345(2) Å, b = 9.261(4) Å, c = 20.189(8) Å; β = 95.075(8)°) from Minto Block (Ungava peninsula, northern Quebec, Canada), a region characterized by high magnetic anomalies. Crystallographic and X-ray absorption spectroscopy data suggest a prevalent divalent oxidation state for Fe and a disordered Fe 2+ distribution in the two octahedral sites Ml and M2. The real part of magnetic susceptibility shows two peaks at ∼5.2 K and 120 K. However, as demonstrated by AC magnetic susceptibility measurements, the origin of the two effects is different: the peak position of the first one (i.e. the effect revealed at 5.2 K) is frequency-dependent, thus suggesting a spin-glass like behaviour. The effect at 120 K can instead be attributed to the occurrence of diluted phases in mica matrix, such as Fe oxides.