igneous
Mahogany Obsidian
Volcanic glass (SiO2 with Hematite or Magnetite inclusions)
Hardness (Mohs): 5 to 5.5. Color: Reddish-brown with black streaks or spots. Luster: Vitreous to glassy. Crystal structure: Amorphous. Cleavage: None (conchoidal fracture). Specific Gravity: 2.3 to 2.6.
- Color
- Reddish-brown with black streaks or spots
- Luster
- Vitreous to glassy
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Physical properties
Hardness (Mohs): 5 to 5.5. Color: Reddish-brown with black streaks or spots. Luster: Vitreous to glassy. Crystal structure: Amorphous. Cleavage: None (conchoidal fracture). Specific Gravity: 2.3 to 2.6.
Formation & geological history
Formed through rapid cooling of high-silica lava. The reddish mahogany color is caused by the inclusion of hematite or magnetite during the cooling process. Common in volcanic regions.
Uses & applications
Used for making jewelry (cabochons), ornamental carvings, and historically for sharp tools like arrowheads and knives. Also popular in the metaphysical community.
Geological facts
Unlike minerals, obsidian is a 'mineraloid' because it has no crystal structure due to rapid cooling. Historically, obsidian was traded across vast distances by indigenous peoples for stone tool manufacturing.
Field identification & locations
Identify by its glass-like texture, conchoidal fracture patterns (curved surface breaks), and the distinctive red-and-black swirling. Commonly found in Oregon (USA), Mexico, and Japan.
