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basanite An extrusive, mafic igneous rock consisting of a feldspathoid mineral (nepheline, analcite, or leucite), olivine, plagioclase feldspar, pyroxene, and minor accessory minerals. Essentially, the mineralogy is that of a basalt, with the addition of a feldspathoid mineral and olivine. Varieties of basanites are defined by the type of feldspathoid mineral present to give nepheline-basanite, analcite-basanite, and leucite-basanite. These rocks are found in close association with alkali basalts. See also TRACHYBASALT.