igneous
Mahogany Obsidian
Volcanic Glass with Hematite or Magnetite inclusions (SiO2 + Fe2O3)
Hardness: 5-5.5 (Mohs); Color: Dark brown or reddish-brown with black streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.3-2.6
- Hardness
- 5-5
- Color
- Dark brown or reddish-brown with black streaks
- Luster
- Vitreous/Glassy
Identified More igneous →
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Physical properties
Hardness: 5-5.5 (Mohs); Color: Dark brown or reddish-brown with black streaks; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.3-2.6
Formation & geological history
Formed through the rapid cooling of felsic lava, preventing crystal growth. The reddish-brown color is caused by the inclusion of iron oxides like hematite or magnetite during the solidification process.
Uses & applications
Commonly used for jewelry (cabochons and beads), ornamental carvings, and by collectors. Historically used for making sharp tools and blades.
Geological facts
Obsidian is technically an 'igneous rock' but also a volcanic glass. Mahogany obsidian is prized for its unique undulating patterns that resemble the wood grain of mahogany trees.
Field identification & locations
Identify in the field by its distinct glassy texture and sharp, shell-like (conchoidal) fractures. Found in volcanic regions such as the American Northwest (Oregon), Mexico, and Japan.
