igneous
Polished mahogany obsidian
Volcanic glass; predominantly rhyolitic silica glass (SiO₂-rich)
AI-generated identification · may be incorrectMohs hardness about 5–5.5; glossy vitreous luster, dark brown to black with tan patches, amorphous structure, and no cleavage. The rounded shape indicates tumbling or polishing.
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Physical properties
Mohs hardness about 5–5.5; glossy vitreous luster, dark brown to black with tan patches, amorphous structure, and no cleavage. The rounded shape indicates tumbling or polishing.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot develop, typically during Quaternary volcanic eruptions. Mahogany coloration comes from iron-oxide inclusions or flow-related banding.
Uses & applications
Used for ornamental objects, cabochons, beads, and lapidary carvings; historically fashioned into sharp blades and tools.
Geological facts
Obsidian fractures with a very sharp conchoidal edge and is technically a mineraloid rather than a crystalline mineral. Its appearance can resemble polished brown jasper or slag.
Field identification & locations
Identify by its glassy shine, smooth curved fracture patterns, lack of visible crystals, and relatively low density (about 2.35). Common sources include Mexico, the western United States, Armenia, and Turkey.
