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Obsidian identification and geology

A naturally occurring volcanic glass formed by the rapid cooling of felsic silica-rich lava, resulting in an amorphous solid rather than a crystalline rock. Obsidian is typically black but can be brown, gray, or banded, and it fractures conchoidally to produce extremely sharp edges. It has been used for tools and weapons since the Paleolithic and is the only common naturally occurring glass. Field: petrology. Example: Obsidian Cliff in Yellowstone National Park is a massive obsidian flow that was used by Indigenous peoples as a source of tool-making material for over 11,000 years, with artifacts traded across much of North America.. Related terms: Rhyolite, Volcanic glass, Conchoidal fracture, Pumice.

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
2026-03-30T15:19:42.055955+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 Obsidian mean in geology?
A naturally occurring volcanic glass formed by the rapid cooling of felsic silica-rich lava, resulting in an amorphous solid rather than a crystalline rock. Obsidian is typically black but can be brown, gray, or banded, and it fractures conchoidally to produce extremely sharp edges. It has been used for tools and weapons since the Paleolithic and is the only common naturally occurring glass.
What is an example of Obsidian?
Obsidian Cliff in Yellowstone National Park is a massive obsidian flow that was used by Indigenous peoples as a source of tool-making material for over 11,000 years, with artifacts traded across much of North America.
Which earth-science field uses the term Obsidian?
Obsidian is used in petrology.
Which terms are related to Obsidian?
Related terms in this reference are Rhyolite, Volcanic glass, Conchoidal fracture, Pumice.

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