igneous
Mahogany Obsidian
Volcanic glass containing Hematite or Magnetite (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 through the rapid cooling of rhyolitic lava that is rich in silica and iron. The reddish-brown color is caused by the presence of oxidized hematite or magnetite inclusions during cooling. Most specimens are from the Cenozoic era.
Uses & applications
Used primarily in lapidary work for jewelry (cabochons, beads), decorative carvings, and metaphysical collecting. Historically used for sharp tools and arrowheads.
Geological facts
Obsidian is technically a 'mineraloid' rather than a mineral because it lacks a crystal structure. Mahogany obsidian is prized for its unique 'wood-grain' pattern, which makes every piece unique.
Field identification & locations
Identify in the field by its distinctive glassy appearance and sharp, curved (conchoidal) edges. It is commonly found in volcanic regions of Mexico, the United States (Oregon, California), and Japan.
