igneous
Mahogany Obsidian
Volcanic Glass (predominantly SiO2 with Hematite/Magnetite inclusions)
Hardness: 5-5.5 (Mohs scale). Color: Black and reddish-brown (mahogany) streaking. Luster: Vitreous to glassy. Structure: Amorphous (non-crystalline). Fracture: Conchoidal. Specific Gravity: 2.3-2.6.
- Hardness
- 5-5
- Color
- Black and reddish-brown (mahogany) streaking
- Luster
- Vitreous to glassy
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Physical properties
Hardness: 5-5.5 (Mohs scale). Color: Black and reddish-brown (mahogany) streaking. Luster: Vitreous to glassy. Structure: Amorphous (non-crystalline). Fracture: Conchoidal. Specific Gravity: 2.3-2.6.
Formation & geological history
Formed from the rapid cooling of silica-rich rhyolitic lava. The mahogany coloring is caused by high concentrations of iron oxide (hematite) or magnetite during the solidification process.
Uses & applications
Primarily used in jewelry, lapidary arts, and ornamental carvings. Historically used for sharp tools and arrowheads. Also valued in the metaphysical market.
Geological facts
Obsidian forms so quickly that crystals do not have time to grow, making it a natural glass. The reddish-brown swirls are known as 'flow banding' and show how the lava was mixing as it cooled.
Field identification & locations
Identify by its glass-like texture and sharp, curved conchoidal fractures. Commonly found in volcanic regions of the Western United States (Oregon, California) and Mexico.
