igneous
Polished black obsidian
Volcanic glass, predominantly rhyolitic silica (SiO₂)
AI-generated identification · may be incorrectTypically black, vitreous, and noncrystalline, with conchoidal fracture; Mohs hardness about 5–5.5 and specific gravity 2.35–2.65. The rounded, glossy piece appears polished or tumbled, though surface reflections obscure diagnostic detail.
Identified More igneous →
Explore Polished black obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically black, vitreous, and noncrystalline, with conchoidal fracture; Mohs hardness about 5–5.5 and specific gravity 2.35–2.65. The rounded, glossy piece appears polished or tumbled, though surface reflections obscure diagnostic detail.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot grow, commonly during Quaternary volcanic eruptions. Major sources include the western United States, Mexico, Armenia, Iceland, Italy, and Japan.
Uses & applications
Used for ornaments, cabochons, beads, carvings, and decorative objects; historically fashioned into exceptionally sharp blades and arrowheads.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks an ordered crystal lattice. Flow bands, snowflake patterns, or translucent edges can indicate varieties or inclusions.
Field identification & locations
Identify by its uniform glassy luster, very smooth conchoidal fracture, lack of visible grains, and sharp edges when freshly broken; rule out black glass or slag, which may show bubbles or manufacturing textures.
