igneous
Polished banded obsidian
Volcanic glass, predominantly SiO₂; likely banded or mahogany obsidian
AI-generated identification · may be incorrectHardness about 5–5.5 Mohs; black, brown, and translucent golden bands with vitreous luster, conchoidal fracture, and no cleavage. The surface appears polished and the specimen may contain flow-banded volcanic glass or crystallites.
Identified More igneous →
Explore Polished banded obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness about 5–5.5 Mohs; black, brown, and translucent golden bands with vitreous luster, conchoidal fracture, and no cleavage. The surface appears polished and the specimen may contain flow-banded volcanic glass or crystallites.
Formation & geological history
Forms when silica-rich lava cools rapidly, preventing normal crystal growth; flow banding develops as viscous magma moves before quenching. Most examples are Quaternary to relatively young, commonly associated with volcanic domes and lava flows.
Uses & applications
Used for cabochons, carvings, ornaments, and lapidary collectibles; historically shaped into sharp tools and projectile points. Its value is mainly decorative rather than industrial.
Geological facts
Obsidian is technically natural glass, not a crystalline rock, though it is classified as igneous. Golden or brown translucent zones may reflect iron-rich coloration, bubbles, or flow structures.
Field identification & locations
Identify by its glassy sheen, sharp conchoidal fractures, smooth polish, and lack of visible mineral grains; it is commonly found in volcanic regions such as Mexico, the western United States, Armenia, and Japan. This image most likely shows a polished, flow-banded variety.
