igneous
Polished mahogany obsidian
Volcanic glass; predominantly silica-rich rhyolitic composition (SiO₂)
AI-generated identification · may be incorrectHardness about 5–5.5 Mohs; dark reddish-brown to mahogany with abundant pale, snowflake-like flow or spherulitic inclusions; vitreous luster, conchoidal fracture, and no cleavage. The rounded, glossy surface indicates tumbling or polishing.
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Physical properties
Hardness about 5–5.5 Mohs; dark reddish-brown to mahogany with abundant pale, snowflake-like flow or spherulitic inclusions; vitreous luster, conchoidal fracture, and no cleavage. The rounded, glossy surface indicates tumbling or polishing.
Formation & geological history
Formed when viscous, silica-rich lava cooled rapidly, preventing crystal growth; the mahogany coloration reflects iron oxides, while pale inclusions commonly represent feldspar-rich spherulites. Most specimens are Quaternary to younger volcanic material.
Uses & applications
Used for lapidary cabochons, beads, carvings, polished stones, and metaphysical collectibles; generally unsuitable for major construction because it is glassy and brittle.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks an ordered crystal lattice. Its conchoidal fracture can produce exceptionally sharp edges.
Field identification & locations
Identify by its glassy luster, smooth conchoidal breaks, lack of visible crystal grains, and dark mahogany-and-black patterning; notable sources include Oregon, Utah, Arizona, Mexico, and Armenia. Avoid strong impacts, which can chip the piece.
