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Silicate minerals

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


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Journal ArticleDOI
TL;DR: The role of H2O in the petrogenesis of pegmatites has been investigated in this paper, where it is argued that the mineral growth in pegmatite petroglobalization is accelerated by the retention of the mineral's liquidus.
Abstract: Granite pegmatite sheets in the continental crust are characterized by very large crystals. There has been a shift in viewing pegmatites as products of very slow cooling of granite melts to viewing them as products of crystal growth in undercooled liquids. With this shift there has been a renewed debate about the role of H2O in the petrogenesis of pegmatites. Based on data on nucleation of minerals and new viscosity models for hydrous granite melts, it is argued that H2O is the essential component in the petrogenesis of granite pegmatites. H2O is key to reducing the viscosity of granite melts, which enhances their transport within the crust. It also dramatically reduces the glass transition temperature, which permits crystallization of melts at hundreds of degrees below the thermodynamic solidus, which has been demonstrated by fluid inclusion studies and other geothermometers. Published experimental data show that because H2O drastically reduces the nucleation rates of silicate minerals, the minerals may not be able to nucleate until melt is substantially undercooled. In a rapidly cooling intrusion, nucleation starts at its highly undercooled margins, followed by inward crystal growth towards its slower-cooling, hotter core. Delay in nucleation may be caused by competition for crystallization by several minerals in the near-eutectic melts and by the very different structures of minerals and the highly hydrated melts. Once a mineral nucleates, however, it may grow rapidly to a size that is determined by the distance between the site of nucleation and the point in the magma at which the temperature is approximately that of the mineral’s liquidus, assuming components necessary for mineral growth are available along the growth path. Granite pegmatites are apparently able to retain H2O during most of their crystallization histories within the confinement of their wall rocks. Pegmatitic texture is a consequence of delayed nucleation and rapid growth at large undercooling, both of which are facilitated by high H2O (±Li, B, F and P) contents in granite pegmatite melts. Without retention of H2O the conditions for pegmatitic textural growth may be difficult to achieve. Loss of H2O due to decompression and venting leads to microcrystalline texture and potentially glass during rapid cooling as seen in rhyolites. In contrast, slow cooling within a large magma chamber promotes continuous exsolution of H2O from crystallizing magma, growth of equant crystals, and final solidification at the thermodynamic solidus. These are the characteristics of normal granites that distinguish them from pegmatites.

102 citations

Book ChapterDOI
TL;DR: In this article, seismic velocities in the transition zone of the mid-ocean ridge basalt are consistent with significant hydration (one half percent or more H 2 O by weight in a pyrolite-composition mantle) and they indicate that lateral velocity variations in the TZ may reflect variations in hydration rather than variations in temperature.
Abstract: Deep reservoirs of water incorporated as hydroxyl into solid silicate minerals of the Earth's interior may contain the majority of the planet's hydrogen and have acted as buffers to maintain ocean volume and continental freeboard over geologic time Two tenths of one weight percent H 2 O in subducted oceanic crustal material and subsequently released to the hydrosphere from mid-ocean ridge basalt is sufficient to recycle the total ocean volume once over 45 billion years It is possible that actual fluxes are several times this amount The nominally anhydrous minerals of the transition zone (410-660 km depth) may serve as a large internal reservoir New and recent data on molar volumes and elastic properties indicate that hydration has a larger effect on shear velocities than does temperature within their respective uncertainties Based on these new data, seismic velocities ill this region are consistent with significant hydration (one-half percent or more H 2 O by weight in a pyrolite-composition mantle) The data indicate that lateral velocity variations in the Transition Zone (TZ) may reflect variations in hydration rather than variations in temperature, at least in regions distant from subduction zones

102 citations

Journal Article
TL;DR: In this article, an infrared spectroscopic study of desert varnish, manganese dendrites, river deposits, and other Manganese oxide concentrations of the terrestrial weathering environment has shown that the morphological distinctions among them have a sound basis in differences in their mineralogy.
Abstract: Infrared spectroscopic study of desert varnish, manganese dendrites, river deposits, and other manganese oxide concentrations of the terrestrial weathering environment has shown that the morphological distinctions among them have a sound basis in differences in their mineralogy. The manganese oxide in manganese dendrites collected in surface exposures is either romanechite or a hollandite-group mineral. These are mixed with varying amounts of silicate minerals, which are a passive substrate for the oxide deposition. Dendrites collected in underground mine workings are todorokite. Manganese stream deposits are generally birnessite with minor amounts of silicate minerals; one nsutite stream deposit has been identified. Crack deposit mineralogy resembles that of manganese dendrites. Cave and subglacial deposit mineralogy resembles that of manganese stream deposits. Although dendrites have long been considered to be pyrolusite, no example of pyrolusite mineralogy has been identified.

102 citations

Journal ArticleDOI
TL;DR: A variety of silicate-CIF3 reaction experiments have been performed in order to determine the rate of reaction and minimum temperatures for which there is complete liberation of oxygen as discussed by the authors.
Abstract: A variety of silicate-CIF3 reaction experiments have been performed in order to determine the rate of reaction and minimum temperatures for which there is complete liberation of oxygen. Fast reaction rates ( ⩽ 2 hr.) and low minimum reaction temperatures ( ∼ 450°C) are shown by minerals such as quartz, feldspar, biotite and pyroxene while garnet reacts much slower and requires higher temperatures (4–8 hr. and 600°C, respectively). It is not possible to completely liberate oxygen from Mg-rich olivine using CIF3. A comparison of δ18O-values obtained from incomplete oxygen extractions to those for complete extractions indicates that a minimum oxygen yield of 95% is required for accurate δ18Odeterminations. These results indicate that CIF3 should not be used as a reagent when attempting to liberate oxygen preferentially from one mineral in a multi-mineral sample.

101 citations

Journal ArticleDOI
TL;DR: The properties of chondrites can be interpreted in terms of metamorphic equilibration and recrystallization of primary chondritic matter, although alternative hypotheses exist as mentioned in this paper.

101 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202344
202264
202153
202064
201951
201865