alkali basalt

rock

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June 18, 2026

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Alkali basalt is a type of extrusive igneous rock that is dark-colored and rich in iron and magnesium, with a low silica content. It is one of two main chemical and petrographic classifications of basalt, the other being tholeiitic basalt.1

Alkali basalts typically contain olivine and a diopsidic or titaniferous augite. They are commonly found in ocean basins and on the forelands and backlands of mountain belts. In some cases, alkali basalts can contain feldspathoid minerals like nepheline, analcime, or leucite, leading to classifications such as nepheline-basalt or leucite-basalt. These rocks are often fine-grained and dark-colored.1

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basalt
Normal alkali basalt contains olivine and, commonly, a diopsidic or titaniferous augite. Alkali basalts predominate among the lavas of the ocean basins and are common among the mafic lavas of the forelands and backlands of the mountain belts. In the Brito-Icelandic province the Paleogene and Neogene…
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Normal alkali basalt contains olivine and, commonly, a diopsidic or titaniferous augite. Alkali basalts predominate among the lavas of the ocean basins and are common among the mafic lavas of the forelands and backlands of the mountain belts. In the Brito-Icelandic province the Paleogene and Neogene…
Read More