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Extrusive identification and geology

Describing igneous rock that formed from magma erupted at the Earth's surface as lava or pyroclastic material , as opposed to intrusive rock that crystallized below the surface. Extrusive rocks are characterized by fine-grained aphanitic or glassy textures due to rapid cooling, and they may contain vesicles from trapped gas bubbles. Common extrusive rocks include basalt, andesite, dacite, and rhyolite. Field: petrology. Example: The Deccan Traps of India are a massive stack of extrusive basalt flows covering over 500,000 km², erupted approximately 66 million years ago near the time of the end-Cretaceous mass extinction.. Related terms: Intrusive, Volcanic, Aphanitic, Lava.

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
2026-03-30T15:19:41.999576+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 Extrusive mean in geology?
Describing igneous rock that formed from magma erupted at the Earth's surface as lava or pyroclastic material , as opposed to intrusive rock that crystallized below the surface. Extrusive rocks are characterized by fine-grained aphanitic or glassy textures due to rapid cooling, and they may contain vesicles from trapped gas bubbles. Common extrusive rocks include basalt, andesite, dacite, and rhyolite.
What is an example of Extrusive?
The Deccan Traps of India are a massive stack of extrusive basalt flows covering over 500,000 km², erupted approximately 66 million years ago near the time of the end-Cretaceous mass extinction.
Which earth-science field uses the term Extrusive?
Extrusive is used in petrology.
Which terms are related to Extrusive?
Related terms in this reference are Intrusive, Volcanic, Aphanitic, Lava.

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