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Basalt identification and geology

A dark-colored, fine-grained aphanitic mafic volcanic rock with a silica content of approximately 45–52% by weight, composed primarily of plagioclase feldspar and pyroxene, with or without olivine. Basalt is the most abundant volcanic rock on Earth and forms the bulk of the oceanic crust, mid-ocean ridges, oceanic islands, and large igneous provinces. It is the extrusive equivalent of gabbro. Field: petrology. Example: The Columbia River Basalt Group in the Pacific Northwest covers over 200,000 km² with lava flows up to 30 m thick, representing one of the largest flood basalt provinces on Earth.. Related terms: Gabbro, Mafic, Mid-ocean ridge, Flood basalt.

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Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T15:19:41.970235+00:00
Review status
Published; not independently peer-reviewed
  • USGS Thesaurus — U.S. Geological Survey. Controlled earth-science terminology used to describe USGS information resources.
  • Glossary of Geologic Terms — U.S. National Park Service. Geologic definitions prepared by the NPS Geologic Resources Inventory.

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Common questions

What does Basalt mean in geology?
A dark-colored, fine-grained aphanitic mafic volcanic rock with a silica content of approximately 45–52% by weight, composed primarily of plagioclase feldspar and pyroxene, with or without olivine. Basalt is the most abundant volcanic rock on Earth and forms the bulk of the oceanic crust, mid-ocean ridges, oceanic islands, and large igneous provinces. It is the extrusive equivalent of gabbro.
What is an example of Basalt?
The Columbia River Basalt Group in the Pacific Northwest covers over 200,000 km² with lava flows up to 30 m thick, representing one of the largest flood basalt provinces on Earth.
Which earth-science field uses the term Basalt?
Basalt is used in petrology.
Which terms are related to Basalt?
Related terms in this reference are Gabbro, Mafic, Mid-ocean ridge, Flood basalt.

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