igneous
Mahogany Obsidian
Volcanic Glass (SiO2 + Fe2O3)
Hardness: 5-5.5 on Mohs scale; Color: Reddish-brown with black inclusions; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.
- Hardness
- 5-5
- Color
- Reddish-brown with black inclusions
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 on Mohs scale; Color: Reddish-brown with black inclusions; 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 where crystallization does not occur. The 'mahogany' color is caused by the presence of oxidized hematite or magnetite inclusions during the cooling process.
Uses & applications
Used primarily for jewelry (cabochons, beads), decorative carvings, meditation stones, and historically for making sharp tools like arrowheads and scalpel blades.
Geological facts
Despite its appearance, obsidian is a volcanic glass rather than a mineral because it lacks a crystalline structure. Ancient cultures prized it for its ability to produce an edge sharper than surgical steel.
Field identification & locations
Identify in the field by its glassy texture, conchoidal (shell-like) fractures, and distinct brownish-red swirls against black. Commonly found in volcanic regions of Mexico, the United States (Oregon and California), and Japan.
