Topic
Silicate minerals
About: Silicate minerals is a research topic. Over the lifetime, 1794 publications have been published within this topic receiving 67064 citations.
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TL;DR: High-alumina minerals refer, in this paper, to Al-rich, normal sedimentary phases, including gibbsite, boehmite, diaspore, possibly "proto-diaspore" and "Proto-alunite", and corundum, in association with kaolin minerals.
Abstract: High-alumina minerals refer, in this paper, to Al-rich, normal sedimentary phases, including gibbsite, boehmite, diaspore, possibly “proto-diaspore” and “proto-alunite”, “Al-chlorite”, and corundum, in association with kaolin minerals. They may be derived from any common Al-containing rock. Processes of origin include direct bauxitization of non-clay silicate minerals and rocks, and the desilication of any of the common clay minerals, particularly of the kaolin group. Apparently aluminous gels were formed within certain marshy basins, and/or were transported into basins, giving rise to concretionary masses of high-alumina minerals. Concretionary deposits were formed by dissolution of Al and reprecipitation.
30 citations
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TL;DR: In this article, a sample of fine-grained sand containing mineral impurities was subjected to bio-leaching with Bacillus spp. strains and subsequent elutriation.
30 citations
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TL;DR: Carbonatites define the largest range in Fe isotope compositions yet measured for igneous rocks, recording significant isotopic fractionations between carbonate, oxide, and silicate minerals during generation in the mantle and subsequent differentiation as discussed by the authors.
Abstract: Carbonatites define the largest range in Fe isotope compositions yet measured for igneous rocks, recording significant isotopic fractionations between carbonate, oxide, and silicate minerals during generation in the mantle and subsequent differentiation. In contrast to the relatively restricted range in δ56Fe values for mantle-derived basaltic magmas (δ56Fe = 0.0 ± 0.1‰), calcite from carbonatites have δ56Fe values between −1.0 and +0.8‰, similar to the range defined by whole-rock samples of carbonatites. Based on expected carbonate-silicate fractionation factors at igneous or mantle temperatures, carbonatite magmas that have modestly negative δ56Fe values of ~ −0.3‰ or lower can be explained by equilibrium with a silicate mantle. More negative δ56Fe values were probably produced by differentiation processes, including crystal fractionation and liquid immiscibility. Positive δ56Fe values for carbonatites are, however, unexpected, and such values seem to likely reflect interaction between low-Fe carbonates and Fe3+-rich fluids at igneous or near-igneous temperatures; the expected δ56Fe values for Fe2+-bearing fluids are too low to produced the observed positive δ56Fe values of some carbonatites, indicating that Fe isotopes may be a valuable tracer of redox conditions in carbonatite complexes. Further evidence for fluid-rock or fluid-magma interactions comes from the common occurrence of Fe isotope disequilibrium among carbonate, oxide, silicate, and sulfide minerals in the majority of the carbonatites studied. The common occurrence of Fe isotope disequilibrium among minerals in carbonatites may also indicate mixing of phenocyrsts from distinct magmas. Expulsion of Fe3+-rich brines into metasomatic aureols that surround carbonatite complexes are expected to produce high-δ56Fe fenites, but this has yet to be tested.
30 citations
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TL;DR: In this article, it is demonstrated that X-ray photoelectron diffraction can be used to differentiate between equivalent, near-equivalent, and nonequivalent sites occupied by two elements either in one single crystal or in crystals of closely similar structure, even when the element(s) concerned comprise only a small fraction of the crystal and when the sub-lattice lacks both long and short-range order.
Abstract: Angle-resolved X-ray photoelectron spectra of freshly exposed cleavage planes of muscovite, lepidolite, phlogopite, and both natural and Pb-exchanged vermiculite are interpreted to yield both quantitative elemental analyses relating to the outermost 100 A of the crystals and a wealth of structural information, the latter from consideration of phenomena resulting from diffraction of the photo-emitted electrons. It is demonstrated that X-ray photoelectron diffraction can be used to differentiate between equivalent, near-equivalent, and non-equivalent sites occupied by two (or more) elements either in one single crystal or in crystals of closely similar structure, even when the element(s) concerned comprise only a small fraction of the crystal and when the sub-lattice lacks both long- and short-range order. These studies are complemented by extensive chemical analyses, by energy-dispersive X-ray (K-emission) analyses performed in an electron microscope (an elementary calibration procedure for which is outlined) and by X-ray diffraction studies. The muscovite and lepidolite are shown to cleave in regions exhibiting typical bulk composition, whereas the phlogopite and vermiculite both cleave in regions rich in aluminium, and deficient in magnesium (relative to their silicon content). The principal interlayer cations in the vermiculite, potassium and calcium, could be entirely replaced with lead by prolonged refluxing in lead nitrate solution: the lead and calcium are shown to retain their hydration spheres whereas potassium coordinates directly (without hydration) to the layer oxygen, as in the true micas. Some structural implications of these data are evaluated and discussed.
30 citations
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TL;DR: In this paper, a model expanding clay, Wyoming montmorillonite, SWy-2, to high pressure CO2 resulted in the formation of a mineral carbonate phase via dry CO2-clay mineral interactions at two different temperatures.
30 citations