Showing papers on "Silicate minerals published in 1978"

Synthesis of iron layer silicate minerals under natural conditions

Abstract: The low temperature synthesis of iron silicate minerals with clay structures is possible at surface temperatures only under reducing conditions. Under oxidizing conditions clay minerals could not be synthesized. Instead quartz and quartzine were found in these X-ray amorphous Fe III hydroxide-silica precipitates after 14 days at low temperatures (20 ~ and 3~ as well as geothite or X-ray amorphous iron hydroxides. Only from solutions containing Fe-II could the different iron-containing clay minerals be built up within days at low temperatures. The presence of Fe-II enables an octahedral layer of the hrucite-gibbsite type to be formed. This is necessary for the bidimensional orientation of SiO4-tetrahedra leading to clay mineral formation. The presence of Fe ~§ and/or Mg2+-ions is necessary for the formation of the A13+- and Fea+-containing octahedral layers. The reducing conditions were obtained in the experiments by addition of dithionite. With a high content of silica (ca. 20 ppm SiO2, 7 ppm Fe) nontronite and lembergite, the di-Fe-III and tri-Fe-II octahedral, three-layer silicates, were built up in several days at low temperatures. With a lower silica content, that is, a lower Si/Fe ratio (15 ppm SiO2 and 20 ppm Fe), the two-layer silicate minerals greenalite and chamosite could be synthesized. A higher Mg content and more reducing conditions in the solutions favored the tri- as well as dioctahedral chamosite synthesis. The conditions of formation of recent naturally formed nontronite fit well with the synthesis conditions. Chamosites in sedimentary iron ores are characterized by a low content of SiO2, between 15-30% SiO2. This low content of silica cannot be the result of primary precipitation from seawater. The iron and silica ratio in seawater or in river waters would lead to a precipitation of ~60% SiO2 in the iron hydroxide precipitates. A probable origin for chamosite iron ores, which explains the low SiO2 content, is diagenesis of the lateritic weathering crust. Indeed, investigations of recent tropical shoreline sediments and in particular their trace element content confirm that cliamosite minerals have formed diagenetically from lateritic panicles in reducing sediments.

Silane coated silicate minerals and method for preparing same

Abstract: Phyllosilicate minerals which exhibit in their structure, sequentially, octahedral layers containing magnesium, aluminum and/or iron oxides and tetrahedral layers of silica, are superficially etched with dilute acid to remove the outer octahedral layer under controlled conditions which preserve the basic structural integrity of the mineral substrate. The acid etch exposes silanol groups on the outer silicate layer of the mineral so that they become available to form silicon-to-oxygen-to-silicon-to-carbon bonds through condensation with organo-silanes. The condensation of the organo-silane with the conditioned mineral surface is accomplished by mixing the acid etched silicate mineral with the organo-silane in a suitable solvent system under mild conditions. The organo-silane may be chosen from either of two classes: those which impart an oleophilic surface to the mineral; or those which enable the mineral surface to form additional chemical bonds with reactive sites within certain polymers and prepolymers. The mineral products of this invention which have been treated to possess oleophilic surfaces are superior additives for rheology control in lubricants, polyolefins, paints and oil well drilling fluids, as well as heat and moisture resistant reinforcing agents for rubbers; while those mineral products treated to possess surfaces chemically reactive with polymers and prepolymers when incorporated in such systems impart to the finished composites improved mechanical properties and heat and moisture resistance.

Weathering of rocks

Abstract: The mechanisms of physical and chemical weathering are reviewed. The breakdown of silicate minerals to secondary crystalline phases is described with reference to the mobilities of the common ions, ion fixation, leaching, influence of crystal structure and environmental factors. The chemical weathering products of common rock types are outlined. (A)

Pyrohydrolysis for the rapid determination of chlorine traces in silicate and non-silicate minerals and rocks

Abstract: This simple method for the determination of chloride takes a total time of 15 min. Samples are mixed with silica in the ratio 1∶1, and the chloride is liberated in an induction furnace by pyrohydrolysis within ca. 10 min. The chloride is collected in a 0.020 M sodium-hydroxide solution. This solution is filled up to 200 ml with twice distilled water and absorption is measured with ferric ammonium sulphate and mercury(II) thiocyanate solution by a Zeiss Elko II photometer. Analysis of three international reference samples show excellent accuracy with a standard deviation of less than 4% (e.g. for a chloride content of 117 ppm in Andesite AGV-1).

Mineral and organic distributions and relationships across the Green River formation's saline depositional center, Piceance Creek Basin, Colorado

Abstract: Stratigraphically correlated profiles of organic matter concentration and profiles of 8 major mineral x-ray diffraction peak heights in oil shales, through Colorado's Green River Formation near its saline depositional center, are presented in histogram form. The profiles are used to show distributions and relationships of the minerals and organic matter. Strong direct relationships between the volume of organic matter in Colorado's Green River Formation oil shales and the relative amounts of the silicate minerals--quartz, soda feldspar, and potash feldspar-- were demonstrated singly and collectively. The silicate minerals were also shown to be directly related to each other. Dawsonite in the saline zone of the Formation was also shown to be directly related to the volume of organic matter and indirectly to the amount of nahcolite. These relationships were all interpreted as the results of CO/sub 2/ evolution from organic matter in the sediment. A strong direct relationship demonstrated between dawsonite and quartz was credited to both the organic CO/sub 2/ mechanisms and to ash-fall decomposition. Significant non-correlation with organic matter or any of the other minerals was found for calcite and analcime. Lack of significant correlation among any of the components in one particular section demonstrated absence of geochemical controlmore » during its deposition. The relationships provide an additional interpretive tool for the Green River Formation.« less

Trimethylgermyl derivatives for the study of silicate structures

Abstract: Silicate minerals react with trimethylchlorogermane in the presence of water to yield trimethylgermyl derivatives SixOy(GeMe3)z; the method is a useful adjunct to the technique of trimethylsilylation for the study of silicate structures.

The Residual Deposits

Abstract: The residual deposits are the insoluble products of rock weathering which have escaped distribution by transporting agencies, and which still mantle the rocks from which they have been derived. Their components belong to two classes, namely, unaltered minerals from the original rocks, and the insoluble products of decomposition. The nature of the minerals of the first class depends upon that of the bedrock, but quartz, felspars, and muscovite are amongst the commonest, although the felspars are usually much decayed. The rarer durable constituents of rocks, such minerals as zircon, rutile, garnet, tourmaline, kyanite, etc., and various iron oxides, magnetite, haematite, ilmenite, and chromite, are also to be found. The silicate minerals comprised in the second class are chiefly hydrous aluminium silicates of the kaolinite-halloysite group, hydrous magnesium silicates of the serpentine-talc group, chlorites and hydromicas, zeolites, and the epidote minerals. Various hydrated oxides of iron and aluminium, and colloidal silica, may also be present.

Recovery of minerals from ultrabasic rocks

Abstract: OF THE DISCLOSURE A process for the metallurgical treatment of pyroxenite-type ore, which comprises comminuting the ore to a particle size range of between about 40 and 600 micron, or alternatively between about 40 to 1000 micron, and thereafter subjecting the comminuted ore to dry HIMS to recover a non-attracted apatite concentrate from weakly attracted silicate minerals contained in the proxenite ore. Another aspect of the invention relates to the recovery of phlogopite and/or vermiculite from more weakly attracted diopside and non-attracted apatite by dry HIMS. A further aspect of the invention relates to particle size fractionation by pneumatic classification followed by dry HIMS, electrostatic separation and dry HIMS, and electrostatic separation alone, applied res-pectively to fine, medium, and coarse particle size fractions respectively to recover apatite from sili-cate minerals contained in pyroxenite ore.

Trace-element distribution and ore formation in vein-metasomatised peridotite at Kalskaret, near Tafjord, South Norway

Abstract: The concentration profiles of the trace elements, S, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Sr, and Y have been determined across a metasomatic vein in peridotite. The introduced elements Ti, V, Sr, and Y show specific enrichment in particular silicate phases in accordance with the availability of suitable lattice sites. In contrast, the other introduced trace elements (Cu and S) behave more like the redistributed elements, Cr, Ni, Mn, and Co which do not show concentration ‘fronts’ that can be simply related to the silicate minerals. Concentration of pentlandite, chalcopyrite, and Cr-magnetite near the boundary between the enstatite and anthophyllite zones gives rise to maxima in the Ni, Cu, S, and Cr distributions, while in the chlorite zone significant concentrations of Cr and Ni occur in the chlorite itself. Control of the distribution of Ni, Cu, and Cr is ascribed to the oxidation/reduction reactions involved in the formation of pentlandite, chalcopyrite and Cr-magnetite, together with the critical role of Al in limiting chlorite formation during metasomatism.

Graphical representation of material balance and equilibrium relations for minerals sparingly soluble in H 2 O

Abstract: Material balance and equilibrium relations between H2O-rich fluids and sparingly soluble minerals are important for the understanding of chemical processes operative at the earths surface and within the earths crust. These two aspects of any chemical system are subject to graphical analysis, and a technique is devised to allow visual presentation of congruent and incongruent reactions between solutions and sparingly soluble silicate minerals in multi-component systems. The method also illustrates the changes in a solutions' composition resulting from both congruent and incongruent interactions with solids. The technique is particularly useful when interpreting reactions occurring during dissolution and precipitation experiments and is also valuable when interpreting the chemical history of ground waters and surface waters. Analysis of the system MgO-SiO2-H2O-HCl demonstrates that, under near-surface conditions, brucite and serpentine-group minerals dissolve congruently in high pH (basic) solutions while talc dissolves congruently in moderately basic to acidic solutions. In the system Na2O-Al2O3-SiO2-H2O-HCl, gibbsite dissolves congruently in moderately acidic to highly basic solutions and kaolinite and siliceous clay minerals dissolve congruently only in acidic solutions.

A relationship between phonon conductivity and seismic parameter Φ for silicate minerals

Abstract: The relationship between the phonon conductivity at room temperature (K N ) and the seismic parameter (Φ) for silicate minerals is suggested. The considerations are based on the Debye model of thermal energy transport phenomena in solids and on the ‘seismic equation of state’ for silicates and oxides given byAnderson (1967). The semiempirical relationship is the formK N = 0.43Φ0.82 where Φ is in km2/s2 andK N in mcal/cm s K, and the empirical relationship isK N =(0.528±0.006)Φ −(8.18±2.11). The laboratory data on thermal and elastic properties for several silicates were taken fromHorai andSimmons (1970).