spinel

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spinel,

magnesium aluminum oxide, MgAl2O4, a mineral crystallizing in the isometric system, usually as octahedrons. It occurs as an accessory mineral in basic igneous rocks, in aluminum-rich metamorphic rocks, and in contact-metamorphosed limestones. Common spinel usually ranges in color from dark green to brown or black, but transparent red, blue, and green varieties are found and are used as gemstones; Myanmar and Sri Lanka are the principal producing countries. Much gem-quality spinel is now produced synthetically.

spinel

[spə′nel]
(mineralogy)
MgAl2O4 A colorless, purplish-red, greenish, yellow, or black mineral, usually forming octahedral crystals, and characterized by great hardness; used as a gemstone.
A group of minerals of general formula AB2O4, where A is magnesium, ferrous iron, zinc, or manganese, or a combination of them, and B is aluminum, ferric iron, or chromium.
References in periodicals archive ?
Fabrication of magnesium aluminate (Mg[Al.sub.2][O.sub.4]) spinel foams.
A review on magnesium aluminate (Mg[Al.sub.2][O.sub.4]) spinel: synthesis, processing and applications.
The spectra of veneers treated with magnesium aluminate or aluminum borate were similar to that of the untreated control with the exception of slight weakening of peaks at 1730, 1160, 1370, 1160, and 680 [cm.sup.-1], possibly caused by degradation of hemicelluloses.
Blocks treated with the other oxy-aluminum compounds were less dimensionally stable than those treated with magnesium aluminate, possibly because of the lower weight gains achieved with these treatments (Table 3).
The peaks obtained for oxy-aluminum-treated wood (with the exception of magnesium aluminate) were broadened compared to the untreated control (Figs.