Basalt is typically made up of augite or feldspar with some silica and olivine. A type of igneous rock, basalt can be found on oceanic floors and terrestrial landscapes formed by lava flows.
Basalt is a small-grained rock composed of minerals such as pyroxene and plagioclase. Pyroxene minerals include augite and diopside, and plagioclase minerals include perthite and labradorite. The physical properties of basalt can result in varying textures, ranging from airy pumice-like compositions to dense masses with smooth surfaces. Basalts with a greater amount of nepheline instead of feldspar can have a finer texture than that of basalt with a higher concentration of plagioclasic feldspar. Compared to gabbro, basalt generally has a smooth texture, although many specimens of basalt have a mixed composition where larger crystals are interspersed in a mass of smaller crystals.
When formed under water in oceanic ridges and vents, basalt flows, which are typically made up of alkali basalts, can be widespread. They can combine to form landscapes such as the Columbia River Flood Basalts in the northwestern area of the United States or the Emeishan Traps of China. Basalt is also found extensively on the moon, especially in areas with volcanic activity, such as the Olympus Mons volcano.