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

Wikidata facts

Image: Basalto afanitico e quasi afirico per i rari e minuti fenocristalli.jpg

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Commons category: Basalt
Commons gallery: Basalt
exact match: purl.obolibrary.org/obo/ENVO_01000236

Sources (5)

via Wikidata · CC0

~24 min read

Article

28 sections

Contents

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.