igneous
Polished mahogany obsidian (likely)
Volcanic glass; rhyolitic obsidian, predominantly amorphous SiO₂
AI-generated identification · may be incorrectDark reddish-brown to black, highly glossy vitreous luster, no visible crystals or cleavage; Mohs hardness about 5–5.5, conchoidal fracture, density approximately 2.3–2.6 g/cm³. The rounded, polished shape appears to be a tumbled or cabochon specimen.
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Physical properties
Dark reddish-brown to black, highly glossy vitreous luster, no visible crystals or cleavage; Mohs hardness about 5–5.5, conchoidal fracture, density approximately 2.3–2.6 g/cm³. The rounded, polished shape appears to be a tumbled or cabochon specimen.
Formation & geological history
Forms when silica-rich lava cools rapidly, preventing crystallization; commonly Quaternary to older Cenozoic volcanic material. The mahogany coloration comes from iron-oxide inclusions or bands.
Uses & applications
Used for cabochons, beads, carvings, decorative objects, and historically sharp tools and arrowheads. Usually valued as an ornamental stone rather than a high-end gemstone.
Geological facts
Obsidian is technically volcanic glass, not a crystalline mineral. Its conchoidal fracture can produce exceptionally sharp edges.
Field identification & locations
Identify by its glassy sheen, uniform dark color, lack of grain, and curved fracture; a streak, crystal, or bubbly texture suggests another material. Common sources include Mexico, the western United States, Armenia, and Turkey.
