igneous
Mahogany Obsidian
Volcanic Glass (Silicate: SiO2 + Fe2O3)
Hardness: 5-5.5 (Mohs scale), Color: Brown/Reddish-brown with black streaks, Luster: Vitreous (glassy), Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.3-2.5
- Hardness
- 5-5
Identified More igneous →
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Brown/Reddish-brown with black streaks, Luster: Vitreous (glassy), Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.3-2.5
Formation & geological history
Formed from rhyolitic volcanic lava that cools rapidly, preventing crystal growth. Its distinct reddish-brown color is caused by high concentrations of iron (magnetite or hematite) inclusions trapped within the obsidian during the cooling process.
Uses & applications
Used primarily in lapidary arts for jewelry, beads, and cabochons. Historically used for making tools and sharp blades; modernly used by collectors for its aesthetic and metaphysical properties.
Geological facts
Because it is amorphous and has no crystalline structure, obsidian is technically a 'mineraloid' rather than a true mineral. The 'mahogany' patterns are unique flows of iron-rich impurities within the silica-rich glass.
Field identification & locations
Identify by its glassy texture and characteristic conchoidal (shell-like) fracture patterns. It is commonly found in areas of recent volcanic activity such as the United States (Oregon, California), Mexico, and Japan.
