igneous
Mahogany Obsidian
Obsidian (SiO2 + Fe2O3)
Hardness: 5-5.5 (Mohs scale); Color: Black with reddish-brown streaks or patches; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Black with reddish-brown streaks or patches
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with reddish-brown streaks or patches; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
Formation & geological history
Formed from rapidly cooling felsic lava that contains high levels of silica. The red-brown streaks are caused by inclusions of Hematite or Magnetite (iron oxide). It is typically found in volcanic regions of various geological ages from the Cenozoic era.
Uses & applications
Commonly used in jewelry for beads and cabochons, decorative carvings, and in alternative medicine practices (metaphysical healing). Historically, obsidian was used to make sharp cutting tools.
Geological facts
Unlike minerals, obsidian is a 'mineraloid' because it lacks a crystal structure. Mahogany obsidian specifically gets its name from its similarity to the color of mahogany wood due to the iron-rich inclusions.
Field identification & locations
Identify by its glassy texture and distinct reddish-brown rhythmic swirling or spotting against a dark background. It is commonly found in the United States (Oregon, California), Mexico, and Japan.
