basalt
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Key facts
- Rock.name
- Basalt
- Rock.type
- Igneous
- Rock.image
- Basalt 12 (48674276333).jpg
- Rock.composition
- Mafic: plagioclase, amphibole, and pyroxene
- Rock.composition_secondary
- Sometimes feldspathoids or olivine
via Wikipedia infobox
Article
28 sectionsContents
- Definition and characteristics
- Etymology
- Types
- Petrology
- Geochemistry
- Morphology and textures
- Subaerial eruptions
- Columnar basalt
- Submarine eruptions
- Pillow basalts
- Distribution
- Earth
- Other bodies in the Solar System
- The Moon
- Venus
- Mars
- Vesta
- Io
- Alteration of basalt
- Weathering
- Metamorphism
- Life on basaltic rocks
- Uses
- See also
- References
- Sources
- Further reading
- External links
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt has the same chemical composition and mineralogy as slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of Venus, which cover ~80% of the surface, are basaltic; the lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars.
Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), 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 kilometres and constitute the most voluminous of all volcanic formations.