Albite transformation and geophysical discontinuity
Ath Godelitsas's insight:
Albite (NaAlSi3O8) is an aluminosilicate mineral. Its crystal structure consists of 3-D framework of Al and Si tetrahedral units. We have used Density Functional Theory to investigate the high-pressure behavior of the crystal structure and how it affects the elasticity of albite. The results of this paper indicate elastic softening between 6–8 GPa.
An unanswered question in the RNA world scenario is how sequence information could be transferred during replication of duplex RNA. Without the aid of sophisticated enzymes, strand re-annealing occurs more quickly than template-directed synthesis. Now, a plausible prebiotic solution to this problem is presented, in which a viscous solvent enables information transfer from a gene-length double-stranded template.
This perspective is a very personal account of the history and evolution of experimental trace element partitioning, although I cannot hope to exhaustively cover all aspects of this discipline. Therefore, I emphasise issues with which I am most familiar: (i) partitioning between mafic silicates and silicate melt; (ii) solid metal-liquid metal partitioning – especially the effects of non-metals; and (iii) metal-silicate liquid partitioning. I first entered the field of experimental partitioning as a grad-student in the mid-1970’s and so was able to see some of the growing pains of this discipline up close and personal. Also where appropriate, I will mention applications of experimental partitioning data to geologic and planetary problems.
Mantle melting, which leads to the formation of oceanic and continental crust, together with crust recycling through plate tectonics, are the primary processes that drive the chemical differentiation of the silicate Earth. The present-day mantle, as sampled by oceanic basalts, shows large chemical and isotopic variability bounded by a few end-member compositions. Among these, the HIMU end-member (having a high U/Pb ratio, μ) has been generally considered to represent subducted/recycled basaltic oceanic crust. However, this concept has been challenged by recent studies of the mantle source of HIMU magmas. For example, analyses of olivine phenocrysts in HIMU lavas indicate derivation from the partial melting of peridotite, rather than from the pyroxenitic remnants of recycled oceanic basalt. Here we report data that elucidate the source of these lavas: high-precision trace-element analyses of olivine phenocrysts point to peridotite that has been metasomatized by carbonatite fluids. Moreover, similarities in the trace-element patterns of carbonatitic melt inclusions in diamonds and HIMU lavas indicate that the metasomatism occurred in the subcontinental lithospheric mantle, fused to the base of the continental crust and isolated from mantle convection. Taking into account evidence from sulfur isotope data for Archean to early Proterozoic surface material in the deep HIMU mantle source, a multi-stage evolution is revealed for the HIMU end-member, spanning more than half of Earth’s history. Before entrainment in the convecting mantle, storage in a boundary layer, upwelling as a mantle plume and partial melting to become ocean island basalt, the HIMU source formed as Archean–early Proterozoic subduction-related carbonatite-metasomatized subcontinental lithospheric mantle.
The dispersion and flocculation behavior of muscovite suspensions in the presence of Ca2+ and Mg2+ are relevant for industrial processing of pre-concentrated muscovite from stone coal, a primary source of vanadium. In this study, the dispersion and flocculation behavior were investigated by means of sedimentation, zeta potential, and ion absorption experiments, as well as the force between particles and ion speciation calculations. The results indicated that the dispersion and flocculation behavior of muscovite particles without excess ions were in qualitative agreement with the classical DLVO theory. The muscovite particles aggregated mainly due to basal surface-edge interactions in acidic suspensions but were dispersed in alkaline suspension by electrostatic repulsion of the total particle surface. In acidic suspensions, the ability of muscovite to form dispersions of muscovite was increased with the decrease in the electrostatic attraction between the basal surface and the edge caused by the compression of the electric double layers withCa2+ and Mg2+. In alkaline suspension, the main adsorption form of Ca2+ and Mg2+ on muscovite surface was the ion-hydroxy complexes. The flocculation behavior of muscovite was affected by the static bridge effect of the ion-hydroxy complexes.
In situ kinetic studies of the heterogeneous nucleation and growth behaviors of iron(III) (hydr)oxide, calcium carbonate, and manganese (hydr)oxide minerals in aqueous systems, are reviewed. In particular, the authors utilized simultaneous small-angle and grazing incidence small-angle X-ray scattering (SAXS/GISAXS) to investigate in situ and in real-time the effects of water chemistry and substrate identity on heterogeneously and homogeneously formed nanoscale precipitate size dimensions and total particle volume.
The authors report the CPO pattern and dominant slip system of bridgmanite under conditions that correspond to the uppermost lower mantle (25 gigapascals and 1,873 kelvin) obtained through simple shear deformation experiments using the Kawai-type deformation-DIA apparatus.
From the symmetry-selective probing of molecular bond orientation with nanometer spatial resolution, the authors determined crystalline phases and orientation in aggregates and films of the organic electronic material perylenetetracarboxylic dianhydride.
Bauxite residues contain considerable concentrations of rare-earth elements (REEs) and the recovery of these REEs together with(out) other metals and utilization of the generated residue in other applications (e.g., building materials) can solve the storage problem.
A new type of acidic macrocellular and mesoporous silica–alumina foam is obtained via a one pot alkaline sol–gel route coupled with a concentrated emulsion-based templating technique. The mixed oxide monolith exhibits high surface acidity, translating into excellent performance in the acid-catalyzed dehydrat
Over the Na+-birnessite basal surface the Gb1 structure is highly disturbed as a result of interaction with this birnessite surface. Unraveling of the Gb1 β-sheet at specific turns and a partial unraveling of the α-helix is observed over birnessite, which suggests specific vulnerable residue sites for oxidation or hydrolysis possibly leading to fragmentation.
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