igneous
Mahogany Obsidian
Volcanic Glass with Hematite/Magnetite (SiO2 + Fe2O3)
Hardness: 5-5.5 on Mohs scale; Color: Reddish-brown with black streaks or spots; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.3-2.6
- Hardness
- 5-5
- Color
- Reddish-brown with black streaks or spots
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 on Mohs scale; Color: Reddish-brown with black streaks or spots; Luster: Vitreous (glassy); Crystal 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 reddish-brown color is caused by the inclusion of iron oxides like hematite or magnetite trapped within the glass as it solidified.
Uses & applications
Used in jewelry (beads, cabochons), ornamental carvings, and holistic practices. Historically used for making sharp tools like scrapers and arrowheads.
Geological facts
Unlike minerals, obsidian is a 'mineraloid' because it lacks a crystalline structure due to its rapid cooling from lava. Mahogany obsidian specifically gets its name from its resemblance to mahogany wood.
Field identification & locations
Identify in the field by its distinct glassy texture and classic conchoidal (shell-like) fracture patterns. It is predominantly found in areas of recent volcanic activity such as the Western United States, Mexico, and Japan.
