igneous
Polished mahogany obsidian
Volcanic glass; rhyolitic obsidian (SiO₂-rich, amorphous)
AI-generated identification · may be incorrectMohs hardness about 5–5.5; black to deep mahogany-brown with glossy vitreous luster and conchoidal fracture. It has no crystal structure or cleavage; the brown areas are likely iron-oxide-rich inclusions or flow bands.
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Physical properties
Mohs hardness about 5–5.5; black to deep mahogany-brown with glossy vitreous luster and conchoidal fracture. It has no crystal structure or cleavage; the brown areas are likely iron-oxide-rich inclusions or flow bands.
Formation & geological history
Obsidian forms when silica-rich lava cools rapidly, preventing crystal growth, usually in volcanic domes and flows. It commonly formed during the Quaternary and older Cenozoic eruptions, though exact age requires locality data.
Uses & applications
Used for ornamental objects, cabochons, beads, carvings, and collectible polished specimens; historically shaped into exceptionally sharp tools and projectile points.
Geological facts
The characteristic curved fractures can produce edges sharper than surgical steel, although they are brittle. “Mahogany obsidian” is a trade name for reddish-brown patterned obsidian, not a separate mineral.
Field identification & locations
Identify it by its glassy polish, uniform amorphous appearance, curved fracture surfaces, and lack of visible interlocking crystals; a streak test is usually white or colorless. Common sources include Mexico, the western United States, Armenia, and Turkey.
