It is composed mostly of feldspathoids, pyroxenes, olivine, and calcic plagioclase and forms from magma low in silica and enriched in alkali metal oxides that solidifies rapidly close to the Earth's surface.

Basanite is an aphanitic (fine-grained) igneous rock that is low in silica and enriched in alkali metals.

[1][2] The mineral assembly in basanite is usually abundant feldspathoids (nepheline or leucite), plagioclase, and augite, together with olivine and lesser iron-titanium oxides such as ilmenite and magnetite-ulvospinel; minor alkali feldspar may be present.

[3] The augite contains significantly greater titanium, aluminium and sodium than that in typical tholeiitic basalt.

They are low in silica (42 to 45% SiO2) and high in alkalis (3 to 5.5% Na2O and K2O) compared to basalt, which typically contains more SiO2, as evident on the diagram used for TAS classification.