igneous
Tumbled black obsidian (likely)
Volcanic glass; primarily rhyolitic silica glass (SiO₂-rich, amorphous)
AI-generated identification · may be incorrectTypically black to dark brown, vitreous/glassy luster, conchoidal fracture, no cleavage, and hardness about 5–5.5 Mohs; the rounded edges indicate tumbling or polishing. The specimen is too small and blurred for confident confirmation.
Identified More igneous →
Explore Tumbled black obsidian (likely) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically black to dark brown, vitreous/glassy luster, conchoidal fracture, no cleavage, and hardness about 5–5.5 Mohs; the rounded edges indicate tumbling or polishing. The specimen is too small and blurred for confident confirmation.
Formation & geological history
Forms when silica-rich lava cools extremely rapidly, preventing crystal growth, mainly during Quaternary to recent volcanic eruptions. Common sources include Mexico, the western United States, Armenia, Turkey, and Iceland.
Uses & applications
Used for ornamental objects, cabochons, beads, carvings, and historically sharp cutting tools; not generally used as structural aggregate. Small polished pieces have modest decorative value.
Geological facts
Obsidian can show snowflake, sheen, rainbow, or mahogany patterns caused by crystallites or inclusions. It is technically a mineraloid rather than a true mineral because it lacks a crystal lattice.
Field identification & locations
Look for uniform glassy black color, sharp conchoidal edges, and translucent brown margins under strong light; black tourmaline or slag may look similar but commonly show crystals, bubbles, or metallic texture. A streak, hardness, and close inspection can help distinguish them.
