Silicate minerals

About: Silicate minerals is a research topic. Over the lifetime, 1794 publications have been published within this topic receiving 67064 citations.

High-precision 41K/39K measurements by MC-ICP-MS indicate terrestrial variability of δ41K

Abstract: Potassium is a major component in continental crust, the fourth-most abundant cation in seawater, and a key element in biological processes. Until recently, difficulties with existing analytical techniques hindered our ability to identify natural isotopic variability of potassium isotopes in terrestrial materials. However, measurement precision has greatly improved, and a range of K isotopic compositions has now been demonstrated in natural samples. In this study, we present a new technique for high-precision measurement of K isotopic ratios using high-resolution, cold plasma multi-collector mass spectrometry. We apply this technique to demonstrate natural variability in the ratio of 41K to 39K in a diverse group of geological and biological samples, including silicate and evaporite minerals, seawater, and plant and animal tissues. The total range in 41K/39K ratios is ca. 2.6‰, with a long-term external reproducibility of 0.17‰ (2σ, N = 108). Seawater and seawater-derived evaporite minerals are systematically enriched in 41K compared to silicate minerals by ca. 0.6‰, a result consistent with recent findings. Although our average bulk-silicate Earth value (−0.54‰) is indistinguishable from previously published values, we find systematic δ41K variability in some high-temperature sample suites, particularly those with evidence for the presence of fluids. The δ41K values of biological samples span a range of ca. 1.2‰ between terrestrial mammals, plants, and marine organisms. Implications of terrestrial K isotope variability for the atomic weight of K and K-based geochronology are discussed. Our results indicate that high-precision measurements of stable K isotopes, made using commercially available mass spectrometers, can provide unique insights into the chemistry of potassium in geological and biological systems.

Frequency Distribution of Clay Minerals in Major Great Soil Groups as Related to the Factors of Soil Formation

Abstract: The frequency distribution or relative abundance of minerals in soils varies with the five principal classes of factors that govern soil formation. The characteristics of the minerals of the parent material, the time factor, climatic factors, relief factors and biotic factors each can be shown to have important independent effects on clay mineralogy of soils under proper circumstances. The soil parent material exerts a control over the frequency distribution of minerals in soils by introduction of the clay minerals into the soil directly, by controlling the course of chemical weathering in the soil through the relative susceptibility of its minerals to weathering, by furnishing abundant divalent metallic cations, by impediment of drainage, or by acceleration of leaching when highly permeable. The time factor is conspicuous as long times give an advanced degree of weathering even in temperate climates. Climate is important, since highly weathered materials inevitably occur as a result of intense leaching in warm tropical and equatorial climates. Relief is important in concentrating leaching water and metallic cations, in affecting oxidation or reduction. The biotic factor affects minerals conspicuously where an A0, horizon develops and resulting cheluviation moves R2O3 out of the A2 horizon. Inherited minerals such as illite, quartz, feldspars, ferro-magnesian minerals, carbonates and gypsum are most abundant in clays of little-weathered parent materials and soils of the zonal Desert, Brown, Chestnut and Tundra soils as well as intrazonal Mountain groups and azonal Regosols and Lithosols. Secondary layer silicate minerals such as vermiculite, secondary chlorite, montmorillonite, kaolinite and halloysite are most abundant in clays of moderately weathered parent materials and soils of the zonal Chernozem, Prairie, Gray—Brown Podzolic, Podzol, Red—Yellow Podzolic, and Low Humic Latosol groups as well as intrazonal Planosol, Rendzina, Dark Magnesium soil, and Wiesenboden groups. Secondary sesquioxide minerals such as hematite, goethite, allophane, gibbsite and anatase and residual resistant primary minerals such as ilmenite and magnetite predominate in the more highly weathered parent materials and soils of the zonal Ferruginous Humic Latosols, Hydrol Humic Latosols, Latosolic Brown, and Ando soils and Laterites, as well as the intrazonal Tropical Savannah and Ground Water Podzol ortstein soils.