Showing papers on "Silicate minerals published in 1980"

Authigenic layer silicate minerals in borehole Elmore 1, Salton Sea Geothermal Field, California, USA

Abstract: A combined petrographic/X-ray/electron microprobe and energy dispersive system investigation of sandstone cuttings from borehole Elmore # 1 near the center of the Salton Sea Geothermal Field has revealed numerous regular variations in the composition, texture, mineralogy and proportions of the authigenic layer silicate minerals in the temperature interval 185° C (411.5 m depth) to 361° C (2,169 m). At temperatures near 190° C, dolomite/ankerite+calcite-bearing sandstones contain an illite/mixed layer phase with 10% expandable layers (dolomite/ankerite zone). In shale, the percentage of expandable layers in the mixed layer phase changes from 10–15% at 185° C to 5% at 210° C (494 m). In the interval 250° C (620 m) to 325° C (1,135 m), the calcite+pyrite+epidote-bearing sandstones contain a layer silicate assemblage of chlorite and illite (chlorite-calcite zone). In the shallower portions of this metamorphic zone, the illite contains 0–5% expandable layers, while at depths greater than 725 m (275° C) it is completely free of expandable layers. On increasing temperature, the white mica shows regular decreases in SiIV, Mg and Fe, and increase in AlIV, AlVI, and interlayer occupancy, as it changes gradually from fine-grained illite (=textural sericite) to coarse-grained recrystallized phengitic white mica. In the same interval, chlorite shows decreases in AlVI and octahedral vacancies and an increase in total Mg+Fe. The sandstones range from relatively unmodified detrital-textured rocks with porosities up to 20% and high contents of illite near 250° C to relatively dense hornfelsic-textured rocks with trace amounts of chlorite and phengite and porosities near 5% at 325° C. Numerous complex reactions among detrital (allogenic) biotite, chlorite, and muscovite, and authigenic illite and chlorite, occur in the chlorite-calcite zone. Biotite appears, and calcite disappears, at a temperature near 325° C and a depth of 1,135m. The biotite zone so produced persists to 360° C in sandstone, at which temperature orthoclase disappears and andradite garnet appears at a depth near 2,155 m. Throughout the biotite zone and into the garnet zone, the biotite undergoes compositional changes that are very similar to those observed in illite/phengite in the chlorite-calcite zone, including increases in interlayer occupancy, AlIV, AlVI, and Ti, and decreases in F−, SiIV, and Mg/Fet+Mg, on increasing temperature. Biotite thus changes from a siliceous, K-deficient biotite at the biotite isograd to a typical low-grade metamorphic biotite at temperatures near 360° C. Minor amounts of talc appear with biotite at the biotite isograd in sandstone, while actinolite appears in both sandstone and shale at temperatures near 340° C (1,325 m). Chlorite completely disappears from sandstone at temperatures of approximately 350° C (1,500 m), and diminishes abruptly in amount in the more chloritic shales at the same depth.

Mixed-Valence Minerals of Iron and Titanium: Correlations of Structural, Mössbauer and Electronic Spectral Data

Abstract: A large cariety of mixed-valence silicate and oxide minerals occur in rocks from the Earth, Moon and Meteorites, They frequently contain Fe2+ -Fe3+, Ti3+ -Ti4+ and Fe2+ -Ti4+ assemblages and often display anomalous color or opacity, high thermal and electrical conductives, and unusual spectral variations with temperature or pressure. Such properties are not attributable to transitions in single cations and indicate the presence of intervalence transitions. The intervalence transitions are observed either as charge transfer (CT) bands in the visible-near infrared region and frequently cause blue colors in FeFe2+ -Fe3+ and Fe2+ -Ti4+ bearing minerals (e.g. viviante, sapphire, dordierite, kyanite, bearing minerals (e.g. vivianite, sapphire, cordierite, kyanite glaucophane, aquamarine), or as electron decolalozation (ED) often causing opacity and semiconductor behavior (e.g. magnetite, ilvaite, deerite, riebeckite). Many of the physical and spectral properties of mixed-valence silicate and oxide minerals may be correlated with crystal structure features and site Occupancies of the metals. Structural variables which affect properties of mixed-valence oxide and silicate minerals or distorted octahedra, tetrahedra, dodecahedra), type of polyhedral linkage (e.g. face-shared, edge-shared, corner-shared) metal-oxygen (M-O) distances, metal-metal (M-M) distances, and M-O-M bond angles; and orientation and extend of linked polyhedra (e.g. isolated pairs, chains, bands, sheets; blocking by Mg2+ and AI3+ in solid solution series). These features may be used to interpret the temperature and pressure dependencies of CT bands in minerals with isolated Fe2+-Fe3+ and Fe2+-Ti4+ clustes (e.g. vivianite, sapphire, glaucophane, kyanite, cordierite, omphacite, pyroxenes, etc.), and the occurance of Fe in intermediate electronic environments in minerals with infinite chains of edge-shared Fe2+-Fe3+ polyhedra (e.g. magnetite, ilvaite, deerite, schorlomite garnets, riebeckite, and potentially aenigmatite, howieite, babingtonite).

Fluorine distribution in the hydrous silicate minerals of the Franklin Marble, Orange County, New York

Abstract: Fifty specimens of the hydrous silicates norbergite, chondrodite, phlogopite, tremolite, edenite, and pargasite from 34 localities in the Franklin Marble of Orange County, New York, were analyzed quantitatively, and their F/(F + Cl + OH) ratios (X.) determined. The average F /(F + Cl + OH) ratio (XF) determined for each species follows the sequence: Xo Trem < Xo phlog < Xo Amph < X. Chond < X. Norb where Xo Amph is the average Xo for amphibole species other than tremolite. The fluorine contents of the hydrous silicate minerals formed within the Franklin Marble are high by comparison with analyses of the same species from other localities. The Franklin Marble is a high-temperature (836 + 40'C), high-pressure (4-7 kbar) metacarbonate. We suggest that the high fluorine content of the tremolite samples has iacreased the upper thermal stability limit for this species, thus preserving the assemblage tremolite + quartz + calcite under granulite facies conditions. There is an ilverse relationship between the F/(F + Cl + OH) ratio and titanium content for chondrodite. This relationship has been noted by earlier investigators for other members of the humite group. The inverse relationship is not evident for Ti values below 0.02 atoms per formula unit.

Mineralogical and Geochemical Transformation of Clays During Catagenesis and Their Relation to Oil Generation

Abstract: Catagenesis of the Upon burial of the sediments, the concentration of expandable 2:1 layer silicates, kaolinite and amorphous inorganic material decreases while illite increases in concentration in the 2.0 μm fraction. The same trend is observed in the 4+ by Al3+ and the ensuing absorption of K+ and occurs prior to the onset of hydrocarbon generation from the sedimentary organic matter. Water is not only released to the pore system by clay dehydration but also by dissolution of amorphous inorganic matter and destruction of layer silicate minerals. Only the last of these mechanisms is operative within the zone of oil generation.

High temperature crystal field spectra of transition metal-bearing minerals - Relevance to remote-sensed spectra of planetary surfaces

Abstract: It is pointed out that transition metal ions in silicate minerals, glasses, and crystalline and amorphous oxyhydroxides and salts contribute to the visible-near infrared spectral profiles of planetary surfaces. Investigations are conducted to obtain spectral information which might be helpful in the interpretation of the remote-sensed spectra of planetary surfaces. A description is presented of the results of high temperature crystal field spectral measurements of a variety of heated minerals containing Cr(3+), Fe(3+), Fe(++), and Mn(++) ions in different coordination symmetries, taking into account a correlation of the temperature-induced variations with those previously observed for octahedrally coordinated Fe(++)-bearing silicates. The employed experimental methods are also discussed, giving attention to the preparation of the samples, the determination of the absorption spectra, electron microprobe analyses, and the curve fitting procedure.

Deterioration of Architectural Structures and Monuments

Abstract: Natural stone, concrete and mortar are the common materials exposed at the facade of architectural structures. Carbonate and silicate minerals are the essential constituents of these materials. These minerals are susceptible to attack by atmospheric CO2. The weathering of these minerals has increased at an alarming rate in the industrial countries due to N02 and S02 emanations.

Melting Property of MgO Containing Sinter

Abstract: The solution property of MgO containing materials into the CaO-Fe2O3 system and the melting property of MgO containing sinter during reduction were investigated. The results obtained are summarized as follows:(1) The formation of high viscosity silicate and magnetite prevents the homogenization of slag and therefore, Cr slag and Ni slag remain unslagged. The formation of dicalcium ferrite prevents the dissolution of periclase into the CaO-Fe2O3 system.(2) During reduction unslagged MgO makes the shell of MgO-FeO solid solution with FeO in glassy silicate and its solution is negligibly low.(3) For both normal sinter and pellet, all silicate minerals dissolve above about 1240°C.(4) MgO addition in sinter is effective to decrease the slag quantity during reduction but the melting property of sinter is not so improved as that of pellet. The proper basicity for sinter and pellet is about 1.4.

Enthalpy (H/sub T/-H/sub 298/) of anhydrous silicate melts from 1520 to 2600/sup 0/K

Abstract: As an aid to modeling the behavior of melted rock at high temperatures, we measured the enthalpy, H/sub T/-H/sub 298/, of anhydrous melts of six silicate rock samples and three silicate minerals for values of temperature T from 1520 to 2600/sup 0/K. The rock samples were basalt, tuff, rhyolite, and desert alluvium from the Department of Energy's Nevada Test Site. The minerals were SiO/sub 2/, CaSiO/sub 3/, and CaMgSi/sub 2/O/sub 6/. We observed a slight compositional dependence of enthalpy for the rock melts. Relative values of enthalpy above 1600/sup 0/K are as follows: enthalpy of basalt > enthalpy of rhyolite > enthalpy of tuff. The measured enthalpies of the molten CaSiO/sub 3/ and CaMgSi/sub 2/O/sub 6/ are significantly higher than enthalpies calculated from additivity relations assuming solid oxide components. Since we cannot predict the behavior of high-temperature silicate liquids from the known behavior (at lower temperatures) of their solid components, we need to acquire more high-temperature experimental data on silicate liquids as a basis for realistic modeling of melted rock behavior.

Diagenetic Features in Sulphides of Dariba-Rajpura Deposit, Udaipur District, Rajasthan

Abstract: Mineralisation is mainly confined to kyanite-graphite-quartz-mica schist, meta chert (chert and its recrystallised form) at places interbanded with quartzite, calc silicate rock, and impure marble. Sulphide ores reveal a variety of diagenetic structures: diagenetic dykes, diagenetic fracture filling, stylolite seams in sulphide-cherty rock and cementation of silicate minerals by sulphide grains.