igneous
Tumbled black stone, likely black obsidian
Obsidian — natural volcanic glass, predominantly silica-rich rhyolitic composition
AI-generated identification · may be incorrectTypically black, opaque, and vitreous to subdued glassy luster; hardness about 5–5.5 Mohs, no crystal structure or cleavage, conchoidal fracture, and specific gravity around 2.3–2.6. The rounded edges indicate tumbling or polishing.
Identified More igneous →
Explore Tumbled black stone, likely black obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically black, opaque, and vitreous to subdued glassy luster; hardness about 5–5.5 Mohs, no crystal structure or cleavage, conchoidal fracture, and specific gravity around 2.3–2.6. The rounded edges indicate tumbling or polishing.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot develop, commonly during Quaternary volcanic eruptions. Major sources include Mexico, the western United States, Armenia, Turkey, and Iceland.
Uses & applications
Used for ornamental carvings, cabochons, beads, arrowheads, and decorative objects; historically fashioned into exceptionally sharp cutting tools. Small polished pieces generally have modest value.
Geological facts
Obsidian is technically volcanic glass rather than a fully crystalline mineral. Similar-looking black stones may include basalt, black jasper, tourmaline, or manufactured glass.
Field identification & locations
Look for uniform glassy black color, conchoidal fracture, sharp chips, and absence of visible grains; a scratch test and inspection for bubbles can help distinguish it from glass, though this image alone is not definitive. Commonly found near rhyolitic lava flows.
