Thermochemical and compressibility data are used to calculate the approximate pressures and temperatures required for the reaction of clinoenstatite to Mg•SiO• (spinel or olivine) or to periclase and stishovite, the reaction of forsteritc to Mg•SiO• (spinel) or periclase and stishovite, and the breakdown of Mg•SiO• (spinel) to periclase and stishovite. The calculated reaction lines for Mg•SiO• ...

Geologists usually deal with rocks that are up to several thousand million years old. They try to reconstruct the tectonic settings where these rocks were formed and the history of events that affected them through the geological time. The spinel group minerals provide useful information regarding the geological environment in which the host rocks were formed. They constitute excellent indicato...

Compact Type A (CTA) inclusions are extremely melilite-rich (typically ~90 vol%), with moderate amounts of spinel and minor fassaite and perovskite. Because CTAs are one of the major types of coarsegrained inclusions found in CV3 chondrites but have not been thoroughly studied as a group, we have undertaken a comprehensive petrographic, mineralchemical, and trace element study of a large suite ...

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 ...

TWO different spinels, analyses of which are given, occur in the layered ultramafic rocks at Dawros. Chrome spinel occurs both as gravity-stratified cumulates and as complex orbs, while an Al-rich spinel is both in rocks of the main Dawros magmatic sequence and in an association with an aluminous bronzite, which may originate by recrystallization. It is concluded that while the chrome spinel is...

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...

Spinels are compounds that have the general formula AB2O4 where A and B are metallic cations. The formal charges of A and B are strictly specifi ed and they are a criterion of the spinel type. There are three types of spinel compounds, the so-called 2-3, 4-2 and 6-1 spinels, where the numbers indicate the formal charges of the cations. The fi rst cation of each pair occupies a tetrahedral site ...

OBJECTIVES Aim of the study was to analyze the mold filling capacity and the dimensional accuracy of a spinel-based investment for titanium castings. METHODS Expansion of the investment in dependence of the preheating temperature was measured in a dilatometer. The degree of transformation of MgO and Al2O3 to spinel (MgAl2O4) was evaluated by means of X-ray powder diffraction. Mold filling cap...

Stabilization efficiencies of spinel-based construction ceramics incorporating simulated nickel-laden waste sludge were evaluated and the leaching behavior of products investigated. To simulate the process of immobilization, nickel oxide was mixed alternatively with gamma-alumina, kaolinite, and hematite. These tailoring precursors are commonly used to prepare construction ceramics in the build...

Introduction: Extraterrestrial spinel is a magnetic mineral that is found in melted micrometeorites, in the fusion crust of meteorites and meteoroid ablation droplets, and in various impact-derived spherules more or less preserved in marine sediments. This mineral can be distinguished from terrestrial spinel on the basis of high Ni content and a high ferric/ferrous ratio resulting from crystall...