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Silicate Minerals (silicate + mineral)
Selected AbstractsBuffering an Acidic Stream in New Hampshire with a Silicate MineralRESTORATION ECOLOGY, Issue 3 2004Gene E. Likens Abstract Ground and pelletized Wollastonite (Wo; CaSiO3) was added to a 50-m reach of an anthropogenically acidified stream within the Hubbard Brook Experimental Forest, New Hampshire, to evaluate its buffering and restoration potential. The Wo was highly effective in raising the pH, acid-neutralizing capacity (ANC), dissolved inorganic carbon (DIC), and Ca2+ concentrations of the stream water, but during the short duration of the experiment had no discernable effect on the stream biota. After initial, spike-like fluctuations in pH and concentrations of ANC, DIC, and Ca2+, the relatively slow dissolution rates of the Wo dampened extreme concentrations and contributed to relatively long-lasting (4 months) amelioration of streamwater acidity. Changes in concentrations of Ca2+, dissolved Si, ANC, and DIC were inversely related to streamflow. After several high, stream-discharge events, concentrations quickly and consistently returned to pre-event conditions. [source] Provenance of sandstones from the Wakino Subgroup of the Lower Cretaceous Kanmon Group, northern Kyushu, JapanISLAND ARC, Issue 1 2000Daniel K. Asiedu Abstract The Wakino Subgroup is a lower stratigraphic unit of the Lower Cretaceous Kanmon Group. Previous studies on provenance of Wakino sediments have mainly concentrated on either petrography of major framework grains or bulk rock geochemistry of shales. This study addresses the provenance of the Wakino sandstones by integrating the petrographic, bulk rock geochemistry, and mineral chemistry approaches. The proportions of framework grains of the Wakino sandstones suggest derivation from either a single geologically heterogeneous source terrane or multiple source areas. Major source lithologies are granitic rocks and high-grade metamorphic rocks but notable amounts of detritus were also derived from felsic, intermediate and mafic volcanic rocks, older sedimentary rocks, and ophiolitic rocks. The heavy mineral assemblage include, in order of decreasing abundance: opaque minerals (ilmenite and magnetite with minor rutile), zircon, garnet, chromian spinel, aluminum silicate mineral (probably andalusite), rutile, epidote, tourmaline and pyroxene. Zircon morphology suggests its derivation from granitic rocks. Chemistry of chromian spinel indicates that the chromian spinel grains were derived from the ultramafic cumulate member of an ophiolite suite. Garnet and ilmenite chemistry suggests their derivation from metamorphic rocks of the epidote-amphibolite to upper amphibolite facies though other source rocks cannot be discounted entirely. Major and trace element data for the Wakino sediments suggest their derivation from igneous and/or metamorphic rocks of felsic composition. The major element compositions suggest that the type of tectonic environment was of an active continental margin. The trace element data indicate that the sediments were derived from crustal rocks with a minor contribution from mantle-derived rocks. The trace element data further suggest that recycled sedimentary rocks are not major contributors of detritus. It appears that the granitic and metamorphic rocks of the Precambrian Ryongnam Massif in South Korea were the major contributors of detritus to the Wakino basin. A minor but significant amount of detritus was derived from the basement rocks of the Akiyoshi and Sangun Terrane. The chromian spinel appears to have been derived from a missing terrane though the ultramafic rocks in the Ogcheon Belt cannot be discounted. [source] Cement Manufacture and the Environment: Part I: Chemistry and TechnologyJOURNAL OF INDUSTRIAL ECOLOGY, Issue 1 2002Hendrik G. van Oss Summary Hydraulic (chiefly portland) cement is the binding agent in concrete and mortar and thus a key component of a country's construction sector. Concrete is arguably the most abundant of all manufactured solid materials. Portland cement is made primarily from finely ground clinker, which itself is composed dominantly of hydraulically active calcium silicate minerals formed through high-temperature burning of limestone and other materials in a kiln. This process requires approximately 1.7 tons of raw materials per ton of clinker produced and yields about 1 ton of carbon dioxide (CO2) emissions, of which cal-cination of limestone and the combustion of fuels each con-tribute about half. The overall level of CO2 output makes the cement industry one of the top two manufacturing industry sources of greenhouse gases; however, in many countries, the cement industry's contribution is a small fraction of that from fossil fuel combustion by power plants and motor vehicles. The nature of clinker and the enormous heat requirements of its manufacture allow the cement industry to consume a wide variety of waste raw materials and fuels, thus providing the opportunity to apply key concepts of industrial ecology, most notably the closing of loops through the use of by-products of other industries (industrial symbiosis). In this article, the chemistry and technology of cement manufacture are summarized. In a forthcoming companion ar-ticle (part II), some of the environmental challenges and op-portunities facing the cement industry are described. Because of the size and scope of the U.S. cement industry, the analysis relies primarily on data and practices from the United States. [source] Reaction-induced nucleation and growth v. grain coarsening in contact metamorphic, impure carbonatesJOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2010A. BERGER Abstract The understanding of the evolution of microstructures in a metamorphic rock requires insights into the nucleation and growth history of individual grains, as well as the coarsening processes of the entire aggregate. These two processes are compared in impure carbonates from the contact metamorphic aureole of the Adamello pluton (N-Italy). As a function of increasing distance from the pluton contact, the investigated samples have peak metamorphic temperatures ranging from the stability field of diopside/tremolite down to diagenetic conditions. All samples consist of calcite as the dominant matrix phase, but additionally contain variable amounts of other minerals, the so-called second phases. These second phases are mostly silicate minerals and can be described in a KCMASHC system (K2O, CaO, MgO, Al2O3, SiO2, H2O, CO2), but with variable K/Mg ratios. The modelled and observed metamorphic evolution of these samples are combined with the quantification of the microstructures, i.e. mean grain sizes and crystal size distributions. Growth of the matrix phase and second phases strongly depends on each other owing to coupled grain coarsening. The matrix phase is controlled by the interparticle distances between the second phases, while the second phases need the matrix grain boundary network for mass transfer processes during both grain coarsening and mineral reactions. Interestingly, similar final mean grain sizes of primary second phase and second phases newly formed by nucleation are observed, although the latter formed later but at higher temperatures. Moreover, different kinetic processes, attributed to different driving forces for growth of the newly nucleated grains in comparison with coarsening processes of the pre-existing phases, must have been involved. Chemically induced driving forces of grain growth during reactions are orders of magnitudes larger compared to surface energy, allowing new reaction products subjected to fast growth rates to attain similar grain sizes as phases which underwent long-term grain coarsening. In contrast, observed variations in grain size of the same mineral in samples with a similar T,t history indicate that transport properties depend not only on the growth and coarsening kinetics of the second phases but also on the microstructure of the dominant matrix phase during coupled grain coarsening. Resulting microstructural phenomena such as overgrowth and therefore preservation of former stable minerals by the matrix phase may provide new constraints on the temporal variation of microstructures and provide a unique source for the interpretation of the evolution of metamorphic microstructures. [source] A new method to calculate end-member thermodynamic properties of minerals from their constituent polyhedra I: enthalpy, entropy and molar volumeJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2005V. J. VAN HINSBERG Abstract The thermodynamic properties of silicate minerals can be described as a linear combination of the fractional properties of their constituent polyhedra. In contrast, given the thermodynamic properties of these polyhedra, the thermodynamic properties of minerals can be estimated, where only the crystallography of the mineral needs to be known. Such estimates are especially powerful for hypothetical mineral end-members or for minerals where experimental determination of their thermodynamic properties is difficult. In this contribution the fractional enthalpy, entropy and molar volume for 35 polyhedra have been determined using weighted multiple linear regression analysis on a data set of published mineral thermodynamic properties. The large number of polyhedra determined, allows calculation of a much larger variety of phases than was previously possible and the larger set of minerals used provides more confident fractional properties. The OH-bearing minerals have been described by partial and total hydroxide coordinated components, which gives better results than previous models and precludes the need of a S,V term to improve estimates of entropy. However, the fractional thermodynamic properties only give adequate results for silicate minerals and double oxides, and should therefore not be used to estimate the properties of other minerals. The thermodynamic properties of ,new' minerals are calculated from a linear stoichiometric combination of their constituent polyhedra, resulting in estimates generally with associated uncertainty of <5%. The quality of such data appears to be of sufficient accuracy for thermodynamic modelling as shown for meta-bauxites from the Alps and the Aegean, where the effect of Zn on the P,T stability of staurolite can be both qualitatively and quantitatively reproduced. [source] The effect of TiO2 and Fe2O3 on metapelitic assemblages at greenschist and amphibolite facies conditions: mineral equilibria calculations in the system K2O,FeO,MgO,Al2O3,SiO2,H2O,TiO2,Fe2O3JOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2000White Mineral equilibria calculations in the system K2O,FeO,MgO,Al2O3,SiO2,H2O,TiO2,Fe2O3 (KFMASHTO) using thermocalc and its internally consistent thermodynamic dataset constrain the effect of TiO2 and Fe2O3 on greenschist and amphibolite facies mineral equilibria in metapelites. The end-member data and activity,composition relationships for biotite and chloritoid, calibrated with natural rock data, and activity,composition data for garnet, calibrated using experimental data, provide new constraints on the effects of TiO2 and Fe2O3 on the stability of these minerals. Thermodynamic models for ilmenite,hematite and magnetite,ulvospinel solid solutions accounting for order,disorder in these phases allow the distribution of TiO2 and Fe2O3 between oxide minerals and silicate minerals to be calculated. The calculations indicate that small to moderate amounts of TiO2 and Fe2O3 in typical metapelitic bulk compositions have little effect on silicate mineral equilibria in metapelites at greenschist to amphibolite facies, compared with those calculated in KFMASH. The addition of large amounts of TiO2 to typical pelitic bulk compositions has little effect on the stability of silicate assemblages; in contrast, rocks rich in Fe2O3 develop a markedly different metamorphic succession from that of common Barrovian sequences. In particular, Fe2O3 -rich metapelites show a marked reduction in the stability fields of staurolite and garnet to higher pressures, in comparison to those predicted by KFMASH grids. [source] The Mineralogical Characteristics of the Lamboglia 2 Roman-Age Amphorae from the Central Adriatic (Croatia),ARCHAEOMETRY, Issue 2 2003I. Sondi The mineralogical characteristics of four Lamboglia 2 Roman-age amphorae excavated from ancient underwater shipwreck localities in the central Adriatic were investigated. X-ray diffraction and optical microscopy analyses showed that the amphorae have similar primary mineral compositions, mainly consisting of quartz, plagioclase, potassium feldspar, diopside, illite and calcite, most probably originating from clayey Eocene flysch deposits used as raw materials in manufacture. The difference in mineral composition between these samples is recognized from the presence or absence of melilite, high-magnesium calcite, aragonite, gypsum and analcime. It was shown that melilite is a secondary mineral formed during the firing process, while the others, which build up through incrustation of marine benthonic communities on the amphora walls and fill the cracks in the amphora bodies, were formed by crystallization in seawater. The firing of the original pieces of amphorae showed that melilite could be formed at temperatures higher than 800°C, most probably through interaction between calcite and silicate minerals present in the raw materials. The presence of melilite, and the absence of illite and calcite, were used to estimate the firing temperature of the amphorae during their production. [source] Special Xenoliths in an Aegirine-Augite Syenite Porphyry in Liuhe, Yunnan, China: Discovery and ImplicationsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2009Xianfan LIU Abstract: Three special types of xenoliths have recently been found in an aegirine-augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies indicate that pure calcite xenocrysts and quartz-bearing topaz pegmatite xenoliths result from the degassing of mantle fluids during their migration, and that black microcrystalline iron-rich silicate-melt xenoliths are the product of the extraction of mantle fluids accompanying degassing and are composed dominantly of quartz, chlorite, and iron-rich columnar and sheet silicate minerals with characteristic minerals, such as native iron, apatite, and zircon. According to the bulk-rock chemical and mineral compositions and crystallization states, the microcrystalline melt xenoliths are not the product of conventional magmatism, and especially the existence of native iron further proves that the xenoliths were mantle fluid materials under reduction or anoxic conditions. The study of the special xenoliths furnishes an important deep-process geochemical background of polymetallic mineralization in different rocks and strata in the study area. [source] | ||||||||||