Topic
Tephroite
About: Tephroite is a research topic. Over the lifetime, 123 publications have been published within this topic receiving 1599 citations.
Papers published on a yearly basis
Papers
TL;DR: In this paper, atomic net charges and electron density distributions of the olivine structures forsterite, fayalite, and tephroite were determined from accurate single-crystal X-ray data on the respective synthetic crystals.
Abstract: Atomic net charges and electron density distributions of the olivine structures forsterite (a-Mg2SiO4), fayalite (a-Fe2SiO4) and tephroite (a-Mn2SiO 4) have been determined from accurate single-crystal X-ray data on the respective synthetic crystals. The atomic net charges were obtained from the direct integration of the electron density within the sphere of a newly defined radius, the effective distribution radius, around each cation. Such net charges revealed that the tetrahedral Si atom is less ionic than the octahedral cations and the transition-metal Fe and Mn are less ionic than Mg. These charges also showed that the M(1)-site cation is less ionic than the M(2)-site cation when the cations of the same kind occupy both M(1) and M(2) sites. * Present address: Department of Earth Sciences, Ehime University, Bunkyo-cho, Matsuyama 790, Japan. 0567-7408/81/030513-06501.00 Radial distributions of valence electrons outside the Ar cores of the transition metals show that the 3d electrons have their maximum densities about 0.4 ~ 0.5 A from the centre of the atom. In three-dimensional difference Fourier maps of forsterite the positive peaks appeared 0.96 A, on average, from the centre of the Si atom along each of the four S i -O directions. [Crystal data: forsterite: a = 4.7534(6), b = 10.1902(15), e = 5.9783 (7)A, space group Pbnm, final R = 0.0209; fayalite: a = 4.8195 (6), b = 10.4788(17), c = 6.0873 (8)A, space group Pbnm, final R = 0.0255; tephroite: a = 4.9023 (6), b = 10,5964 (16), c = 6.2567 (9) A, space group Pbnm, final R = 0.0310.]
186 citations
TL;DR: In this paper, the Raman spectra of the olivine-group minerals have a characteristic set of two intense lines of the Si-O asymmetric stretching band (wavenumber κ1) and Si -O symmetric stretching bands (κ2).
Abstract: Synthetic end-members Mg2SiO4, Fe2SiO4, Mn2SiO4, and Co2SiO4 and natural samples of forsterite-fayalite series, tephroite and monticellite, are investigated using Raman spectroscopy. The Raman spectra of the olivine-group minerals have a characteristic set of two intense lines of the Si-O asymmetric stretching band (wavenumber κ1) and Si-O symmetric stretching band (κ2). The κ1 and κ2 values of the Mg2SiO4-Ca(Mg, Fe)SiO4 series, in which the M2 site is occupied by nontransition elements, vary from 847 cm−1 to 857 cm−1 and from 815 cm−1 to 825 cm−1, respectively, and their ω (= κ1 − κ2) value is fairly constant around 32 cm−1. On the other hand, fayalite, tephroite, and other olivine-group minerals in which transition elements exist in the M2 site have a fairly constant κ1 (836-839 cm−1) value and variable κ2 (808-819 cm−1) and ω (20-32 cm−1) values. The ω value of the forsterite-fayalite series systematically increases with Mg#[= Mg/(Mg + Fe)] and is useful for determining their chemical compositions.
126 citations
TL;DR: In this paper, plane-wave density functional theory (DFT) calculations were performed to simulate water and carbon dioxide adsorption at the (010) surface of five olivine minerals.
74 citations
TL;DR: In this article, the catalytic power of 14 inorganic materials, namely, 4 synthetic short-range ordered oxides, 4 CBD-treated clay minerals, and 6 primary minerals in the abiotic synthesis of humic acids (HA) through the oxidative polymerization of hydroquinone was investigated.
57 citations
TL;DR: In this paper, the polarized micro-Raman spectra for twelve orthosilicate glasses containing varying proportions of Ca2+, Fe2+, Mg2+, and Mn2+, were measured.
Abstract: We have measured polarized micro-Raman spectra for twelve orthosilicate glasses containing varying proportions of Ca2+, Fe2+, Mg2+, and Mn2+, and one FeOSiO2 composition slightly enriched in silica relative to fayalite. We have also obtained selected area electron diffraction data for glasses having the compositions of forsterite (Mg2SiO4), fayalite (Fe2SiO4), and tephroite (Mn2SiO4). Our Raman data indicate that: (1) CaMg olivine glasses all have similar structures consisting of isolated SiO4 tetrahedra with subordinate short-chain polymers; (2) addition of Ca2+ causes reduction in the effective SiO vibrational force constants; (3) in the absence of iron, a proportion of manganese occurs in tetrahedral MnO4 complexes which are not network formers; (4) silicon-oxygen bonds are shorter in glasses than in the isocompositional crystals; (5) significant polymerization occurs in fayalite-bearing glasses. The diffraction results for forsterite glass show evidence for cryptocrystalline periclase regions no larger than 40 A, probably resulting from a melt free oxygen fraction which cannot be quenched to glass. Fayalite and tephroite glass diffraction patterns show no such evidence for a free oxygen fraction. Therefore, it is proposed that the high degree of polymerization of fayalite-bearing glass results from network-forming Fe2+ ions.
52 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 2 |
| 2020 | 3 |
| 2019 | 1 |
| 2017 | 2 |
| 2016 | 2 |
| 2015 | 5 |