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Rachel Roberts - One of the best experts on this subject based on the ideXlab platform.
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Basalt or not? Near-infrared spectra, surface mineralogical estimates, and meteorite analogs for 33 Vp-type asteroids.
The Astronomical Journal, 2018Co-Authors: Paul S. Hardersen, Vishnu Reddy, Edward A. Cloutis, Matt Nowinski, Margaret Dievendorf, Russell M. Genet, Savan Becker, Rachel RobertsAbstract:Investigations of the main asteroid belt and efforts to constrain that population's physical characteristics involve the daunting task of studying hundreds of thousands of small bodies. Taxonomic systems are routinely employed to study the large scale nature of the asteroid belt because they utilize common observational parameters, but asteroid taxonomies only define broadly observable properties and are not compositionally diagnostic (Tholen, 1984; Carvano et al., 2010, Hasselmann et al., 2012). This work builds upon the results of Hardersen et al. (2014, 2015), which has the goal of constraining the abundance and distribution of basaltic asteroids throughout the main asteroid belt. We report on the near infrared (NIR: 0.7 to 2.5 microns) reflectance spectra, surface mineralogical characterizations, spectral band parameter analysis, and meteorite analogs for 33 Vp asteroids. NIR reflectance spectroscopy is an effective remote sensing technique to detect most Pyroxene Group minerals, which are spectrally distinct with two very broad spectral absorptions at 0.9 and 1.9 microns (Cloutis et al., 1986; Gaffey et al., 2002; Burbine et al., 2009). Combined with the results from Hardersen et al. (2014, 2015), we identify basaltic asteroids for 95 percent (39 of 41) of our inner-belt Vp sample, but only 25 percent (2 of 8) of the outer-belt Vp sample. Inner belt basaltic asteroids are most likely associated with 4 Vesta and represent impact fragments ejected from previous collisions. Outer belt Vp asteroids exhibit disparate spectral, mineralogic, and meteorite analog characteristics and likely originate from diverse parent bodies. The discovery of two additional likely basaltic asteroids provides additional evidence for an outer-belt basaltic asteroid population.
Daqiang Cang - One of the best experts on this subject based on the ideXlab platform.
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Complementation in the composition of steel slag and red mud for preparation of novel ceramics
International Journal of Minerals Metallurgy and Materials, 2018Co-Authors: Yanbing Zong, Wen-hui Chen, Yong Fan, Tai-lin Yang, Zhaobo Liu, Daqiang CangAbstract:A method for preparing novel ceramics was developed in this study. Different ratios red muds were added to steel slags to optimize the preparation of novel ceramics by a traditional ceramic preparation process. The sintering mechanism, microstructure, and performance were studied by X-ray diffraction techniques, scanning electron microscopy, and combined experiments of linear shrinkage, water absorption, and flexural strength. The results confirmed that red mud can reduce the volumetric instabilities through the complementarity of red mud and ferroalloy slag. The crystal phases in the ceramics are all Pyroxene Group minerals, including diopside ferrian, augite, and diopside. The flexural strength of the ceramic that contains 40wt% red mud and was prepared at the optimal sintering temperature (1140°C) is greater than 93 MPa; its corresponding water absorption is less than 0.05%.
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Preparation of novel ceramics with high CaO content from steel slag
Materials & Design, 2014Co-Authors: Lihua Zhao, Zhou Yuanyuan, Daqiang CangAbstract:Abstract Steel slag, an industrial waste discharged from steelmaking process, cannot be extensively used in traditional aluminosilicate based ceramics manufacturing for its high content of calcium oxide. In order to efficiently utilize such solid waste, a method of preparing ceramics with high CaO content was put forward. In this paper, steel slag in combination with quartz, talcum, clay and feldspar was converted to a novel ceramic by traditional ceramic process. The sintering mechanism, microstructure and performances were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) techniques, combined experimenting of linear shrinkage, water absorption and flexural strength. The results revealed that all crystal phases in the novel ceramic were Pyroxene Group minerals, including diopsite ferrian, augite and diopsite. Almost all raw materials including quartz joined the reaction and transformed into Pyroxene or glass phase in the sintering process, and different kinds of clays and feldspars had no impact on the final crystal phases. Flexural strength of the ceramic containing 40 wt.% steel slag in raw materials can reach 143 MPa at sintering temperature of 1210 °C and its corresponding water absorption, weight loss, linear shrinkage were 0.02%, 8.8%, 6.0% respectively. Pyroxene Group minerals in ceramics would contribute to the excellent physical and mechanical properties.
Roland Maas - One of the best experts on this subject based on the ideXlab platform.
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High-K andesite petrogenesis and crustal evolution: Evidence from mafic and ultramafic xenoliths, Egmont Volcano (Mt. Taranaki) and comparisons with Ruapehu Volcano, North Island, New Zealand
Geochimica et Cosmochimica Acta, 2016Co-Authors: Richard C. Price, Ian E. M. Smith, Robert B. Stewart, John A. Gamble, Kerstin Gruender, Roland MaasAbstract:Abstract This study uses the geochemistry and petrology of xenoliths to constrain the evolutionary pathways of host magmas at two adjacent andesitic volcanoes in New Zealand’s North Island. Egmont (Mt. Taranaki) is located on the west coast of the North Island and Ruapehu lies 140 km to the east at the southern end of the Taupo Volcanic Zone, the principal locus of subduction-related magmatism in New Zealand. Xenoliths are common in the eruptives of both volcanoes but the xenoliths suites are petrographically and geochemically different. Ruapehu xenoliths are predominantly Pyroxene–plagioclase granulites derived from Mesozoic meta-greywacke basement and the underlying oceanic crust. The xenolith population of Egmont Volcano is more complex. It includes sedimentary, metamorphic and plutonic rocks from the underlying basement but is dominated by coarse grained, mafic and ultramafic igneous rocks. Gabbroic xenoliths (Group 1) are composed of plagioclase, clinoPyroxene and amphibole whereas ultramafic xenoliths are dominated by amphibole (Group 2) or Pyroxene (Group 3) or, in very rare cases, olivine (Group 4). In Group 1 xenoliths plagioclase and clinoPyroxene and in some cases amphibole show cumulate textures. Amphibole also occurs as intercumulate poikilitic crystals or as blebs or laminae replacing Pyroxene. Some Group 2 xenoliths have cumulate textures but near monomineralic amphibole xenoliths are coarse grained with bladed or comb textures. Pyroxene in Group 3 xenoliths has a polygonal granoblastic texture that is commonly overprinted by veining and amphibole replacement. Group 1 and most Group 2 xenoliths have major, trace element and Sr, Nd and Pb isotope compositions indicating affinity with the host volcanic rocks. Geochemical variation can be modelled by assimilation fractional crystallisation (AFC) and fractional crystallisation (FC) of basaltic parents assuming an assimilant with the composition of average crystalline basement and Group 1 xenoliths have compositions approximating the solid material extracted during these processes. Some Group 2 xenoliths have relatively unevolved Sr and Nd isotopic compositions and they are interpreted to have derived as crystal cumulates from a more primitive parental basalt or through metasomatic alteration of other xenolith types by isotopically less evolved fluids or melts. Some Group 3 xenoliths could have originally been Pyroxene cumulates but the granoblastic textures of others are more consistent with an origin as restites generated during anatexis of amphibolite. Group 4 xenoliths have textures similar to those of mantle-derived peridotite xenoliths found in intraplate basalts. The geochemical variation is consistent with a system fed by mantle-derived magmas that underplated and intruded the lower crust. At this level AFC and FC and crustal anatexis generated cumulates and Pyroxene restite represented by the mafic and ultramafic xenoliths. The magmas segregating at these deep levels moved higher into the crust where a complex dispersed magma storage and plumbing system formed. Here magmas evolved further through AFC and FC with the formation of cumulates and crystal mushes that are represented by some Group 1 and Group 2 xenoliths. Xenoliths were further modified by interaction with host magmas or by alteration at the side walls of magma storages and conduits.
Paul S. Hardersen - One of the best experts on this subject based on the ideXlab platform.
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Basalt or not? Near-infrared spectra, surface mineralogical estimates, and meteorite analogs for 33 Vp-type asteroids.
The Astronomical Journal, 2018Co-Authors: Paul S. Hardersen, Vishnu Reddy, Edward A. Cloutis, Matt Nowinski, Margaret Dievendorf, Russell M. Genet, Savan Becker, Rachel RobertsAbstract:Investigations of the main asteroid belt and efforts to constrain that population's physical characteristics involve the daunting task of studying hundreds of thousands of small bodies. Taxonomic systems are routinely employed to study the large scale nature of the asteroid belt because they utilize common observational parameters, but asteroid taxonomies only define broadly observable properties and are not compositionally diagnostic (Tholen, 1984; Carvano et al., 2010, Hasselmann et al., 2012). This work builds upon the results of Hardersen et al. (2014, 2015), which has the goal of constraining the abundance and distribution of basaltic asteroids throughout the main asteroid belt. We report on the near infrared (NIR: 0.7 to 2.5 microns) reflectance spectra, surface mineralogical characterizations, spectral band parameter analysis, and meteorite analogs for 33 Vp asteroids. NIR reflectance spectroscopy is an effective remote sensing technique to detect most Pyroxene Group minerals, which are spectrally distinct with two very broad spectral absorptions at 0.9 and 1.9 microns (Cloutis et al., 1986; Gaffey et al., 2002; Burbine et al., 2009). Combined with the results from Hardersen et al. (2014, 2015), we identify basaltic asteroids for 95 percent (39 of 41) of our inner-belt Vp sample, but only 25 percent (2 of 8) of the outer-belt Vp sample. Inner belt basaltic asteroids are most likely associated with 4 Vesta and represent impact fragments ejected from previous collisions. Outer belt Vp asteroids exhibit disparate spectral, mineralogic, and meteorite analog characteristics and likely originate from diverse parent bodies. The discovery of two additional likely basaltic asteroids provides additional evidence for an outer-belt basaltic asteroid population.
S. L. Chaplot - One of the best experts on this subject based on the ideXlab platform.
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Lattice dynamics, Raman spectroscopy, and inelastic neutron scattering of orthoenstatite Mg 2 Si 2 O 6
Physical Review B, 1998Co-Authors: Narayani Choudhury, Subrata Ghose, C. Pal Chowdhury, Chun-k. Loong, S. L. ChaplotAbstract:Enstatite ${\mathrm{Mg}}_{2}{\mathrm{Si}}_{2}{\mathrm{O}}_{6}$ is an important rock-forming silicate of the Pyroxene Group. It exists in several polymorphs, the structures of which are characterized by double $[{\mathrm{MgO}}_{6}]$ octahedral bands and single silicate chains. This paper reports lattice-dynamical rigid-ion model calculations and polarized Raman and inelastic-neutron-scattering measurements of orthoenstatite ${\mathrm{Mg}}_{2}{\mathrm{Si}}_{2}{\mathrm{O}}_{6},$ which is orthorhombic $(\mathrm{Pbca})$ with 80 atoms in the unit cell. The calculated elastic constants, phonon frequencies, density of states, and specific heat are in good agreement with the experimental data. The optical-phonon branches along the \ensuremath{\Sigma} and \ensuremath{\Delta} directions are relatively flat without significant dispersion, but have moderate dispersion along the \ensuremath{\Lambda} direction, reflecting the strong structural anisotropy in orthoenstatite. Orthoenstatite undergoes a displacive-reconstructive phase transformation at $\ensuremath{\sim}1360\mathrm{K}$ to protoenstatite ${\mathrm{Mg}}_{2}{\mathrm{Si}}_{2}{\mathrm{O}}_{6},$ which is also orthorhombic $(\mathrm{Pbcn})$ with 40 atoms in the unit cell and the $a$ dimension half that of orthoenstatite. However, the computed phonon-dispersion relations in orthoenstatite do not exhibit any lattice instability in the entire Brillouin zone. The calculations predict that at the \ensuremath{\Gamma} point the lowest optic ${A}_{g}$ mode involving translations of ${\mathrm{Mg}}^{2+}$ ions and translations and rotations of the tetrahedral silicate Groups softens from $104{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in protoenstatite to $82{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in orthoenstatite, which is consistent with the single-crystal polarized Raman-scattering measurements. The phonon spectra obtained from inelastic-neutron-scattering measurements have been interpreted on the basis of model calculations. The broad peak in the 20--80-meV range in orthoenstatite is mainly due to Mg translations and the librations of the nearly rigid tetrahedral $[{\mathrm{SiO}}_{4}]$ Groups, whereas the internal Si-O bond stretching vibrations of the $[{\mathrm{SiO}}_{4}]$ Groups contribute mainly above 80 meV. The bridging oxygens in the silicate chains are vibrationally distinct from the nonbridging oxygens, leading to significant differences in the vibrational spectra of orthoenstatite and protoenstatite with tetrahedral silicate chains from those in forsterite ${\mathrm{Mg}}_{2}{\mathrm{SiO}}_{4}$ with isolated silicate tetrahedra. The band gaps found in the phonon density of states of forsterite are filled by the vibrations of the bridging oxygens in the silicate chains in the phonon densities of states of orthoenstatite and protoenstatite.
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Lattice dynamics and Raman spectroscopy of protoenstatite Mg_2Si_2O_6
Physics and Chemistry of Minerals, 1994Co-Authors: Subrata Ghose, Narayani Choudhury, S. L. Chaplot, C. Pal Chowdhury, S. K. SharmaAbstract:Enstatites (Mg_2Si_2O_6) are important rock forming silicates of the Pyroxene Group whose structures are characterised by double MgO_6 octahedral bands and single silicate chains. Orthoenstatite transforms to protoenstatite above 1273 K with a doubling of the a axis and a rearrangement of the silicate chains with respect to the Mg_2+ ions. Lattice dynamical calculations based on a rigid-ion model in the quasi-harmonic approximation provide theoretical estimates of elastic constants, long wavelength phonon modes, phonon dispersion relations, total and partial density of states and inelastic neutron scattering cross-sections of protoenstatite. The computed elastic constants are in good agreement with experimental data. The computed density of states of a chain silicate such as protoenstatite is distinct from that of olivines (forsterite, Mg_2SiO_4 and fayalite, Fe_2-SiO_4) with isolated silicate tetrahedra. The band gaps in the density of states in forsterite are largely due to the separation in the frequency ranges of the external and internal vibrations of the isolated silicate Group, whereas in protoenstatite these gaps are filled by the vibrations of the bridging oxygens of the silicate chain. The computed density of states is used to calculate the specific heat, the mean square atomic displacements and temperature factors. Validity of these calculations are supported by Raman scattering measurements. Polarised and unpolarised Raman spectra are obtained from small single crystals of protoenstatite (Li,Sc)_0.6Mg_1.4Si_2O_6 stable at room temperature using the 488 nm or 514.5 nm lines of an Ar^+ ion laser and a micro-Raman spectrometer with backscattering geometry. The Raman spectra were analysed and interpreted based on the lattice dynamical model. The experimental Raman frequencies and mode assignments (based on polarised single crystal spectra) are in good agreement with those obtained from lattice dynamical calculations.
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Lattice dynamics and Raman spectroscopy of protoenstatite Mg2Si2O6
Physics and Chemistry of Minerals, 1994Co-Authors: Subrata Ghose, Narayani Choudhury, S. L. Chaplot, C. Pal Chowdhury, Suvasini SharmaAbstract:Enstatites (Mg2Si2O6) are important rock forming silicates of the Pyroxene Group whose structures are characterised by double MgO6 octahedral bands and single silicate chains. Orthoenstatite transforms to protoenstatite above 1273 K with a doubling of the a axis and a rearrangement of the silicate chains with respect to the Mg2+ ions. Lattice dynamical calculations based on a rigid-ion model in the quasi-harmonic approximation provide theoretical estimates of elastic constants, long wavelength phonon modes, phonon dispersion relations, total and partial density of states and inelastic neutron scattering cross-sections of protoenstatite. The computed elastic constants are in good agreement with experimental data. The computed density of states of a chain silicate such as protoenstatite is distinct from that of olivines (forsterite, Mg2SiO4 and fayalite, Fe2-SiO4) with isolated silicate tetrahedra. The band gaps in the density of states in forsterite are largely due to the separation in the frequency ranges of the external and internal vibrations of the isolated silicate Group, whereas in protoenstatite these gaps are filled by the vibrations of the bridging oxygens of the silicate chain. The computed density of states is used to calculate the specific heat, the mean square atomic displacements and temperature factors. Validity of these calculations are supported by Raman scattering measurements. Polarised and unpolarised Raman spectra are obtained from small single crystals of protoenstatite (Li,Sc)0.6Mg1.4Si2O6 stable at room temperature using the 488 nm or 514.5 nm lines of an Ar+ ion laser and a micro-Raman spectrometer with backscattering geometry. The Raman spectra were analysed and interpreted based on the lattice dynamical model. The experimental Raman frequencies and mode assignments (based on polarised single crystal spectra) are in good agreement with those obtained from lattice dynamical calculations.
