High-Ti basalt
| Igneous rock | |
 |
|
| Composition | |
|---|---|
| Mafic: amphibole and pyroxene, sometimes plagioclase, feldspathoids, and/or olivine. |
Basalt (pronounced /bəˈsɔːlt/, /ˈbæsɒlt/ or /ˈbæsɔːlt/) is a common extrusive igneous (volcanic) rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of lava basalt flows.
By definition, basalt is an aphanitic (fine-grained) igneous rock with generally 45-53% silica (SiO2) and less than 10% feldspathoid by volume, and where at least 65% of the rock is feldspar in the form of plagioclase. This is as per definition of the International Union of Geological Sciences (IUGS) classification scheme. It is the most common volcanic rock type on Earth, being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands, including Iceland, the Faroe Islands, Réunion and the islands of Hawaii. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains. The average density is 3.0 g/cm3.
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