Silicate minerals

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

Hydrogeological processes controlling the release of arsenic in parts of 24 Parganas district, West Bengal

Abstract: A study was conducted to understand the hydrogeological processes dominating in the North 24 Parganas and South 24 Parganas based on representative 39 groundwater samples collected from selected area. The abundance of major ions was in the order of Ca2+ > Na+ > Mg2+ > K+ > Fe2+ for cations and HCO3 − > PO4 3− > Cl− > SO4 2− > NO3 − for anions. Piper trilinear diagram was plotted to understand the hydrochemical facies. Most of the samples are of Ca-HCO3 type. Based on conventional graphical plots for (Ca + Mg) vs. (SO4 + HCO3) and (Na + K) vs. Cl, it is interpreted that silicate weathering and ion exchange are the dominant processes within the study area. Previous studies have reported quartz, feldspar, illite, and chlorite clay minerals as the major mineral components obtained by the XRD analysis of sediments. Mineralogical investigations by SEM and EDX of aquifer materials have shown the occurrence of arsenic as coating on mineral grains in the silty clay as well as in the sandy layers. Excessive withdrawal of groundwater for irrigation and drinking purposes is responsible for fluctuation of the water table in the West Bengal. Aeration beneath the ground surface caused by fluctuation of the water table may lead to the formation of carbonic acid. Carbonic acid is responsible for the weathering of silicate minerals, and due to the formation of clay as a product of weathering, ion exchange also dominates in the area. These hydrogeological processes may be responsible for the release of arsenic into the groundwater of the study area, which is a part of North 24 Parganas and South 24 Parganas.

Manganese silicate minerals from broken hill, New South Wales

Abstract: Sixteen unpublished analyses of Broken Hill manganese silicates (two pyrox‐mangite, one rhodonite, four hedenbergite, and nine bustamite) from the papers of the late Dr W. T. Schaller are presented. They have been complemented with additional analyses by the electron microprobe to define the compositional fields of these minerals. Data are provided on the relationship of these minerals with tephroite and garnet. The occurrence of roepperite (zincian tephroite) at Broken Hill is discredited, and its validity is doubtful. Dannemorite from Broken Hill has a composition close to Mn2(Fe,Mg)5Si8O22(OH)2, and can be considered a valid amphibole subspecies.

Geochemistry of iron in the Salton Sea, California

Abstract: The Salton Sea is a large, saline, closed-basin lake in southern California. The Sea receives agricultural runoff and, to a lesser extent, municipal wastewater that is high in nutrients, salt, and suspended solids. High sulfate concentrations (4xhigher than that of the ocean), coupled with warm temperatures and low-redox potentials present during much of the year, result in extensive sulfate reduction and hydrogen sulfide production. Hydrogen sulfide formation may have a dramatic effect on the iron (Fe) geochemistry in the Sea. We hypothesized that the Fe(II)-sulfide minerals should dominate the iron mineralogy of the sediments, and plans to increase hypolimnetic aeration would increase the amount of Fe(III)-oxides, which are strong adsorbers of phosphate. Sequential chemical extractions were used to differentiate iron mineralogy in the lake sediments and suspended solids from the tributary rivers. Iron in the river-borne suspended solids was mainly associated with structural iron within silicate clays (70%) and ferric oxides (30%). The iron in the bottom sediments of the lake was associated with silicate minerals (71% of the total iron in the sediments), framboidal pyrite (10%), greigite (11%), and amorphous FeS (5%). The ferric oxide fraction was <4% of the total iron in these anaerobic sediments. The morphological characteristics of the framboidal pyrite as determined using SEM suggest that it formed within the water column and experiences some changes in local redox conditions, probably associated with alternating summer anoxia and the well-mixed and generally well-aerated conditions found during the winter. The prevalence of Fe(II)-sulfide minerals in the sediments and the lack of Fe(III)-oxide minerals, suggest that the classic model of P-retention by Fe(III)-oxides would not be operating in this lake, at least during anoxic summer conditions. Aeration of the hypolimnion could affect the internal loading of P by changing the relative amounts of Fe(II)-sulfides and Fe(III)-oxides at the sediment/water interface.

New Ways of Characterizing Layered Silicates and their Intercalates

Abstract: Four new methods of probing the atomic and microstructural characteristics of the clay minerals are described: solid-state, magic-angle-spinning 27 Al and 29 Si n.m.r. (along with 18 C n.m.r. of mobile, intercalated organic species); X-ray induced photoelectron studies encompassing photoelectron diffraction as a complement to conventional photoelectron spectroscopy; high-resolution electron microscopy either alone or in association with electron-stimulated X-ray emission microanalysis; and neutron scattering techniques. In reviewing the principles, scope and application of these methods specific case histories are selected from representative minerals belonging to the serpentines, kandites, smectites, micas, vermiculites, chloritoids, zeolites and intergrowths of these with one another or with other silicate minerals. Emphasis is placed on problems not readily amenable to solution by traditional, X-ray based procedures.