Igneous
Mahogany Obsidian
Volcanic Glass with Hematite/Magnetite inclusions (SiO2 + Fe2O3)
Hardness: 5-5.5 (Mohs scale); Color: Black with mottled streaks or splotches of reddish-brown; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.3-2.6
- Hardness
- 5-5
- Color
- Black with mottled streaks or splotches of reddish-brown
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with mottled streaks or splotches of reddish-brown; Luster: Vitreous (glassy); Crystal structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.3-2.6
Formation & geological history
Formed from extrusive volcanic activity where felsic lava cools rapidly with minimal crystal growth. The mahogany color is caused by the inclusion of iron oxides (hematite or magnetite) that become trapped during the cooling process. Most specimens are relatively young geologically, typically from the Cenozoic era.
Uses & applications
Commonly used for lapidary work, including spheres (like the one pictured), cabochons, and beads. It is also used in decorative carvings, feng shui practices, and increasingly in surgical scalpel manufacturing due to its ability to create an edge thinner than steel.
Geological facts
Because it has no crystal structure, obsidian breaks with extremely sharp, curved edges. For millennia, it was the preferred material for making spearheads and arrowheads. Mahogany obsidian is considered one of the 'gentler' forms of obsidian in metaphysical circles.
Field identification & locations
Identify in the field by its glassy texture and distinctive conchoidal (shell-like) fracture patterns. It is found in areas of recent volcanic activity, most notably in the United States (Oregon, Utah, Arizona, California), Mexico, and Japan. Collectors look for high contrast between the red and black bands.
