metaluminous

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metaluminous Applied to igneous rocks in which there are fewer molecules of Al2O3 than of (CaO + Na2O + K2O). ‘Metaluminous’, together with the terms ‘peraluminous’ and ‘peralkaline’, describe the alumina saturation of an igneous rock, portraying variations in what is usually the second most abundant oxide component in the rock (after silica).