igneous
Likely obsidian (volcanic glass)
Obsidian; naturally occurring silica-rich volcanic glass, typically rhyolitic in composition
AI-generated identification · may be incorrectBlack, glossy, with smooth conchoidal fractures and no visible crystals; hardness about 5–5.5 Mohs. The image alone cannot confirm composition; similar-looking industrial glass or slag is possible.
Identified More igneous →
Explore Likely obsidian (volcanic glass) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Black, glossy, with smooth conchoidal fractures and no visible crystals; hardness about 5–5.5 Mohs. The image alone cannot confirm composition; similar-looking industrial glass or slag is possible.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals do not develop, generally in geologically young volcanic settings. The specimen’s age and provenance cannot be determined from the photo.
Uses & applications
Used for ornamental objects, jewelry, and historically for exceptionally sharp cutting tools; small fragments are mainly valued by collectors.
Geological facts
Obsidian breaks with curved, razor-sharp edges and is not a mineral because it lacks an ordered crystal structure.
Field identification & locations
The glossy black surface and curved fracture are consistent with obsidian. Field checks include examining fresh fracture surfaces and looking for flow bands; common sources include volcanic regions such as the western United States, Mexico, and Iceland.
