igneous
Likely obsidian fragment
Volcanic glass, predominantly silica-rich rhyolitic composition (SiO₂-rich)
AI-generated identification · may be incorrectDark gray to black, vitreous luster, conchoidal fracture, and no visible crystals; hardness about 5–5.5 Mohs, with glassy texture and sharp edges. The pale gray streaks may reflect weathering, surface coating, or reflected light.
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Physical properties
Dark gray to black, vitreous luster, conchoidal fracture, and no visible crystals; hardness about 5–5.5 Mohs, with glassy texture and sharp edges. The pale gray streaks may reflect weathering, surface coating, or reflected light.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot develop, commonly in volcanic domes and lava flows. It is generally Quaternary to Cenozoic in age, though obsidian occurs in older volcanic terrains.
Uses & applications
Used historically for extremely sharp tools and projectile points; today it is collected, carved, and occasionally used in jewelry. Common rough fragments usually have modest commercial value.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks an ordered crystal structure. Snowflake, rainbow, mahogany, and sheen varieties result from inclusions or optical effects.
Field identification & locations
Commonly found near rhyolitic volcanoes, including areas of Mexico, the western United States, Armenia, Italy, and Japan. Confirm with its glassy appearance and conchoidal fracture; a steel scratch test is not definitive, and avoid handling sharp edges.
