Turbiditic sandstones from the mid–Late Cretaceous Tianba Flysch sequence are well exposed near Tianba in the north Nieru Valley, southern Tibet, and contain significant amounts of chrome-rich spinels. Microprobe results show that the spinels have a well-developed Fe-Ti trend and have Cr/( ) 0.4–0.65, Mg/( ) 0.3–0.9, and TiO2 2 Cr Al Mg Fe 11%. The occurrence of melt inclusions, and well above ...

Natural Cr-spinels already characterized by X-ray single crystal diffraction and electron microprobe have been analyzed by Raman spectroscopy. The results we report show that there is a strong correlation between the Cr/(Cr+Al) ratio (Cr#) and the A1g mode for the studied spinels. A strong correlation of this mode with Mg/(Mg+Fe) (Mg#) can be seen only for spinels with Mg# higher than 0.60. Oth...

Ti valence measurements in MgAl2O4 spinel from calcium-aluminum-rich inclusions (CAIs) by X-ray absorption near-edge structure (XANES) spectroscopy show that many spinels have predominantly tetravalent Ti, regardless of host phases. The average spinel in Allende type B1 inclusion TS34 has 87% Ti. Most spinels in fluffy type A (FTA) inclusions also have high Ti valence. In contrast, the rims of ...

We investigated the crystal and structural behavior of several Cr-bearing spinels from the Archean chromitites of Amsaga (Mauritania). The chemical and structural data testified a retrograde metamorphism from amphibolite to greenschist facies, witnessed by relative changes in the amount of all the major oxides (Cr, Al, Mg, Fe2+, Fe3+), the relative proportion of Fe/Fetot as well as the structur...

Spinels from cumulus and non-cumulus members of the 0thris ophiolite display a considerable variation in composition. Cumulus pierites and gabbros contain either a primary chromite and/or a reaction spinel formed by reaction with co-existing sili?ate,-" (Cr--A1 varia tion) or intercumulus liquid (Cr--Fe variation). Non-cumulus peridotites contain spinels which vary along a Cr--A1 trend. Harzbur...

A thorough consideration of the relation between the lattice parameters of 185 binary and ternary spinel compounds, on one side, and ionic radii and electronegativities of the constituting ions, on the other side, allowed for establishing a simple empirical model and finding its linear equation, which links together the above-mentioned quantities. The derived equation gives good agreement betwe...

2014 Measurements of the magnetic resonance linewidth 0394H of molybdenum spinels are reported for both paramagnetic and ferromagnetic phases, with particular attention to the region near critical temperature. The magnetic resonance spectra have been measured in the temperature range from 10 K to 300 K with a standard Xband ESR spectrometer. It was shown that the characteristic temperature chan...

Simple algebraic equations show that the bulk compressibility in spinel-type compounds can be expressed by means of cation oxide polyhedral compressibilities and a term that accounts for the pressure effect on the internal oxygen position in the unit cell. The equations explain ~i! the difference of compressibilities at octahedral and tetrahedral sites, ~ii! why the macroscopic bulk modulus can...

Pristine and substituted spinels, Li(M1/6Mn11/6)O4 (M ~ Co1/6, Co1/12Al1/12) were prepared and their cathodic performance up to 80 cycles at ambient temperature and at 50 uC and the Li ion kinetic parameters obtained by galvanostatic intermittent titration technique (GITT) at ambient temperature and 50 uC and electrochemical impedance spectroscopy (EIS) at ambient temperature up to 80 cycles we...

We have conducted an electron microprobe study of minor element distributions among spinels from two type B 1 calcium-aluminum-rich inclusions (CAIs): Allende TS-23 and Leoville 3537-2. We show that by maintaining the petrologic context (edge, middle, and center of the inclusion plus their host silicate phase), four populations of spinels are resolvable based on their minor element contents. On...