igneous
Polished mahogany obsidian
Volcanic glass, primarily rhyolitic composition (SiO₂-rich); mahogany coloration from iron-oxide inclusions
AI-generated identification · may be incorrectHardness about 5–5.5 Mohs; black to reddish-brown patches, vitreous luster, conchoidal fracture, no cleavage, and amorphous (non-crystalline) structure. The rounded, glossy surface indicates tumbling or polishing.
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Physical properties
Hardness about 5–5.5 Mohs; black to reddish-brown patches, vitreous luster, conchoidal fracture, no cleavage, and amorphous (non-crystalline) structure. The rounded, glossy surface indicates tumbling or polishing.
Formation & geological history
Rapid cooling of silica-rich lava prevented crystal growth, while iron oxides produced the mahogany pattern. It is geologically young volcanic material, commonly associated with Quaternary volcanic fields.
Uses & applications
Used for cabochons, carvings, ornamental objects, lapidary work, and inexpensive gemstone specimens; unsuitable for most structural construction because it fractures readily.
Geological facts
Obsidian is natural volcanic glass rather than a true crystalline mineral. Mahogany obsidian is valued for its attractive red-brown flow patterns and polish.
Field identification & locations
Identify by its glassy luster, sharp conchoidal fractures, lack of visible grains, and dark red-brown iron-oxide patches; common sources include Mexico, the western United States, and Armenia.
