Alkali olivine (basalt)
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.
definition of tholeiite and alkali basalt here are more proscriptive 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.
http://en.wikipedia.org/wiki/Basalt; Carmichael, I.S. Turner, F.J., Verhoogen, John, 1974, Igneous petrology: New York, McGraw HIll Book Co., p.42-43.
Parents: Basalt (23)
[Description taken from GeoSciML SimpleLithology201012.rdf]
Category: Analysed material
The different kinds of sample material collected in the field have been classified hierarchically. Examples: “till”, “soil”, “vegetation”. Taken from the “Sample_Types_SHARED” database table.
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