A natural volcanic glass formed when silica-rich lava cools very rapidly. Used by ancient peoples for tools and weapons due to its ability to form extremely sharp edges. Texture: Glassy vitreous. Rock type: Igneous Extrusive. Grain size: None glass. Formation: Forms when silica-rich lava erupts and cools so rapidly that crystals cannot form, resulting in volcanic glass. Common geological settings: Found near recent volcanic activity, especially rhyolitic volcanoes. Notable deposits in Oregon, Mexico, and Turkey. Common look-alikes and related entries: Basalt, Pumice, Rhyolite.
Glassy rocks — Place this specimen in a broader field-identification workflow.
Obsidian vs Basalt — Compare observable properties and safer field tests.
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.
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GeoMiner
Last updated
2026-03-30T14:39:43.130386+00:00
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Published; not independently peer-reviewed
Rocks — U.S. National Park Service. Authoritative overview of rock groups, the rock cycle, and geologic processes.
A natural volcanic glass formed when silica-rich lava cools very rapidly. Used by ancient peoples for tools and weapons due to its ability to form extremely sharp edges.
How can you identify Obsidian?
Compare several properties rather than relying on colour alone. This entry records rock type: Igneous Extrusive; texture: Glassy vitreous; grain size: None glass. Confirm an important identification with additional field tests or qualified laboratory work.
How does Obsidian form?
Forms when silica-rich lava erupts and cools so rapidly that crystals cannot form, resulting in volcanic glass.
Where is Obsidian commonly found?
Found near recent volcanic activity, especially rhyolitic volcanoes. Notable deposits in Oregon, Mexico, and Turkey.
What is Obsidian commonly confused with?
Obsidian may be confused with Basalt, Pumice, Rhyolite. Compare multiple diagnostic properties because colour and surface appearance can overlap.
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