page_title: Basalt
section_title: Morphology and textures
hierarchical_section_title: Basalt / Petrology / Morphology and textures
caption_attribution_description: English: Basalt lava (glowing rock) oozing over basalt lava flow
context_page_description: Basalt is a mafic extrusive igneous rock formed from the rapid cooling of lava rich in magnesium and iron exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt, and the eruption of basalt lava is observed by geologists at about 20 volcanoes per year.
  Molten basalt lava has a low viscosity due to its relatively low silica content, resulting in rapidly moving lava flows that can spread over great areas before cooling and solidifying. Flood basalts are thick sequences of many such flows that can cover hundreds of thousands of square kilometers and constitute the most voluminous of all volcanic formations.
  Basaltic magmas are thought to have their origin in the Earth's upper mantle. The chemistry of basalts thus provides clues to conditions deep in the Earth's interior.
  Basalt is also an important rock type on other planetary bodies in the Solar System; for example, the lunar maria are plains of flood basaltic lava flows, and basalt is a common rock on the surface of Mars.
context_section_description: The shape, structure and texture of a basalt is diagnostic of how and where it erupted—for example, whether into the sea, in an explosive cinder eruption or as creeping pāhoehoe lava flows, the classic image of Hawaiian basalt eruptions.
caption: An active basalt lava flow
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