igneous
Obsidian (likely)
Volcanic glass, predominantly silica-rich rhyolitic composition (no fixed mineral formula)
AI-generated identification · may be incorrectDark gray to black with a glassy luster and conchoidal fracture; hardness about 5–5.5 Mohs. The image shows a small, irregular glassy fragment, but composition cannot be confirmed from appearance alone.
Identified More igneous →
Explore Obsidian (likely) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to black with a glassy luster and conchoidal fracture; hardness about 5–5.5 Mohs. The image shows a small, irregular glassy fragment, but composition cannot be confirmed from appearance alone.
Formation & geological history
Forms when silica-rich lava cools rapidly, preventing crystals from growing. It is generally geologically young and occurs around volcanic flows and domes.
Uses & applications
Used for ornamental objects, jewelry, and historical cutting tools; quality specimens are collected.
Geological facts
Obsidian is natural volcanic glass rather than a crystalline mineral, and sharp flakes can have exceptionally keen edges.
Field identification & locations
Look for a glassy surface, curved shell-like fracture, and typically dark color; common at volcanic sites, including parts of the western United States, Mexico, and Iceland. Similar dark glassy materials can be industrial slag, so field context helps.
