Search results for "petrology"
showing 10 items of 1516 documents
Mn3+ in garnets III. Absence of Jahn-Teller distorition in synthetic Mn3+-bearing garnet
1985
The crystal structure of a ternary Mn3+-bearing garnet, close to the composition Gross34 Spess26 CaMnGt40 has been refined to a weighted R-value of 0.051 for 440 unique reflections. The lattice constant is 11.867(1) A, fractional atomic parameters for oxygen are x=0.0374 (2), y=0.0470 (2), and z=0.6532 (2). Refinement of site occupancies gave 0.81 (3) Ca+0.19 (3) Mn2+ in the eight coordinated site 24c and 0.64 (2) Al+0.36 (2) Mn3+ in the octahedral site 16a. No deviation from the cubic space group Ia3d has been observed, the Mn3+-bearing YO6 octahedron is nearly regular. Thus, the presence of the 3d 4-configurated ion Mn3+ does not cause Jahn-Teller distortion in this garnet structure.
Contrasting evolution of iron phase composition in soils exposed to redox fluctuations
2018
Abstract Ferric iron (FeIII) solid phases serve many functions in soils and sediments, which include providing sorption sites for soil organic matter, nutrients, and pollutants. The reactivity of Fe solid phases depends on the mineral structure, including the overall crystallinity. In redox-active soils and sediments, repeated reductive dissolution with subsequent exposure to aqueous ferrous iron (Fe2+) and oxidative re-precipitation can alter Fe phase crystallinity and reactivity. However, the trajectory of Fe mineral transformation under redox fluctuations is unclear and has been reported to result in both increases and decreases in Fe phase crystallinity. Several factors such as water bu…
A Validation Methodology for a Combined Heating Cooling and Power (CHCP) Pilot Plant
2004
A great number of variables significantly influence the energetic, environmental and economic results of CHP (Combined Heating and Power) and CHCP (Combined Heating Cooling and Power) plants operation, and as a consequence their project activity is rather complex. In order to select the best layout and properly size the machines, detailed data on hourly electric, thermal, and cooling demand are necessary, so that a series of plant life cycle simulations may have to be carried out. Unfortunately, such detailed data are rarely available, because energy consumptions data for existing buildings are usually derived from aggregated monthly or bimonthly gas and electricity bills. Even more difficu…
Humite- and scapolite-bearing assemblages in marbles and calcsilicates of Dronning Maud Land, Antarctica: new data for Gondwana reconstructions
1999
This study investigates marbles and calcsilicates in Central Dronning Maud Land (CDML), East Antarctica. The paleogeographic positioning of CDML as part of Gondwana is still unclear; however, rock types, mineral assemblages, textures and P–T conditions observed in this study are remarkably similar to the Kerala Khondalite Belt in India. The CDML marbles and calcsilicates experienced a Pan-African granulite facies metamorphism at c. 570 Ma and an amphibolite facies retrogression at c. 520 Ma. The highest grade assemblage in marbles is forsterite+spinel+calcite+dolomite, in calcsilicates the assemblages are diopside+spinel, diopside+garnet, scapolite+wollastonite+clinopyroxene±quartz, scapol…
Clay-biosurfactant materials as functional drug delivery systems: Slowing down effect in the in vitro release of cinnamic acid
2017
Abstract The main objectives of the present paper were the preparation and characterization of new surfactant-modified clays and the evaluation of their potential applicability as drug delivery systems for the oral administration of the cinnamic acid (CA) drug. The organoclays (OC) were prepared by loading different amounts of the biocompatible nonionic polyoxyethylene sorbitan monolaurate surfactant (Tween20) onto K10 montmorillonite (Mt) clay and characterized through the construction of the adsorption isotherms by means of the spectrophotometric method. The performance of the prepared material was verified by gathering the adsorption isotherms of the cinnamic acid onto the Mt/Tween20 org…
Geochemistry and origin of ultramafic enclaves and their basanitic host rock from Kula Volcano, Turkey
2013
Abstract The Quaternary Kula Volcanic Province is located in western Anatolia, Turkey. This Na-alkaline anorogenic volcanism includes exposures of around 80 cinder cones, lava flows, and tuffs, representing one of the youngest volcanic activities in this region (1.9–0.026 Ma). The magmatism is related to an extensional regime and is interpreted as being derived predominantly from the asthenospheric mantle. The lava flows are mostly of a basanitic composition and host rare comagmatic enclaves. The enclaves are composed of two dominant lithologies: amphibolites and clinopyroxenites with and without olivine. Amphibole is usually resorbed and replaced by a rhoenite-rich breakdown corona. The mi…
Microstructural evolution of gas hydrates in sedimentary matrices observed with synchrotron X-ray computed tomographic microscopy
2015
The formation process of gas hydrates in sedimentary matrices is of crucial importance for the physical and transport properties of the resulting aggregates. This process has never been observed in situ at submicron resolution. Here we report on synchrotron-based microtomographic studies by which the nucleation and growth processes of gas hydrate were observed at 276 K in various sedimentary matrices such as natural quartz (with and without admixtures of montmorillonite type clay) or glass beads with different surface properties, at varying water saturation. Both juvenile water and metastably gas-enriched water obtained from gas hydrate decomposition was used. Xenon gas was employed to enha…
A computational and experimental investigation of halloysite silicic surface modifications after alkaline treatment
2023
Density functional theory calculations were performed in order to investigate the formation of silanol groups on the outer surface of halloysite nanotubes, as possible products of the reactions with water in alkaline environments. The results, discussed in terms of energy release and structural properties of the modified surface, suggest that the formation of various kinds of silanol group constellations, and even the extraction of orthosilicic acid, are highly exothermic reaction in the presence of hydroxide ions. Thermogravimetric analysis, FT-IR, XRD and X-ray fluorescence spectrometry performed on halloysite treated at high pH conditions indicate that the adsorption of water on the oute…
Characterisation of clayey raw materials for ceramic manufacture in ancient Sicily
2011
Abstract It is well known that mineralogical, petrographic and chemical analyses can successfully support provenance studies of archaeological ceramics. The characterisation of a ceramic paste, the assessment of its technology of production and its provenance assignment related to a specific production centre or to a geographical and/or compositional space, are all tasks that can be performed even more accurately if the clayey raw materials used in pottery production are also studied. For that reason the identification of the clay deposits exploited in a given ceramic workshop often plays a key role in the archaeometric reconstruction of the production cycle where geology, mineralogy, petro…
Post-fragmentation vesiculation timescales in hydrous rhyolitic bombs from Chaitén volcano
2020
Abstract Bubble nucleation and growth dynamics exert a primary control on the explosivity of volcanic eruptions. Numerous theoretical and experimental studies aim to capture the complex process of melt vesiculation, whereas textural studies use vesicle populations to reconstruct magma behaviour. However, post-fragmentation vesiculation in rhyolitic bombs can create final quenched bubble (vesicle) textures that are not representative of the nature of fragmenting magma within the conduit. To examine bubble growth in hydrous rhyolitic bombs, we have used heated stage microscopy to directly observe vesiculation of a Chaiten rhyolite melt (with an initial dissolved water content of ~0.95 wt %) a…