igneous
Mahogany Obsidian
Volcanic Glass (SiO2 + Fe2O3)
Hardness: 5-5.5 (Mohs scale); Color: Dark brown or black with reddish-brown streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.35-2.6.
- Hardness
- 5-5
- Color
- Dark brown or black with reddish-brown streaks
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Dark brown or black with reddish-brown streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.35-2.6.
Formation & geological history
Formed when rhyolitic lava flows cool very quickly, preventing crystal growth. Its distinct reddish-brown color is caused by trace amounts of hematite or magnetite (iron oxide) trapped within the glass. Found in volcanic regions.
Uses & applications
Used primarily for jewelry (cabochons, beads), decorative carvings, and metaphysical healing collections. In pre-history, it was used for razor-sharp tools and weapons.
Geological facts
Obsidian is technically not a mineral but a 'mineraloid' because it lacks a crystal structure. Mahogany obsidian specifically gets its name from the wood-like mahogany color created by iron impurities.
Field identification & locations
Identify by its glass-like texture and characteristic shell-like (conchoidal) fractures. Common in the Western United States (Oregon, California) and Mexico. Collectors should look for distinct reddish mottling against a black background.
