Simple Lithology

alkali olivine basalt

definition Alkali olivine basalt is silica-undersaturated, characterized by the absence of orthopyroxene, absence of quartz, presence of olivine, and typically contains some feldspathoid mineral, alkali feldspar or phlogopite in the groundmass. Feldspar phenocrysts typically are labradorite to andesine in composition. Augite is rich in titanium compared to augite in tholeiitic basalt. Alkali olivine basalt is relatively rich in sodium. more like this
note The definition of tholeiite and alkali basalt here are more prescriptive than those found in most reference authorities. This is to actually provide some descriptive criteria to allow assignment of rocks on a hand sample basis to the tholeiite or alkali basalt categories if detailed petrographic or chemical data are available. more like this
source; Carmichael, I.S. Turner, F.J., Verhoogen, John, 1974, Igneous petrology: New York, McGraw HIll Book Co., p.42-43. more like this
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narrower alkali olivine basalt
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