igneous
Mahogany Obsidian
Obsidian (Volcanic Glass with Hematite/Magnetite inclusions)
Hardness: 5-5.5 (Mohs scale); Color: Black with reddish-brown streaks/swirls; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Black with reddish-brown streaks/swirls
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with reddish-brown streaks/swirls; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6
Formation & geological history
Formed when felsic lava cools rapidly with minimal crystal growth. The mahogany color comes from inclusions of Magnetite or Hematite (iron oxides) during the cooling process. Most specimens are relatively young geologically, typically from the Tertiary or Quaternary periods.
Uses & applications
Used primarily for jewelry (cabochons, beads), decorative carvings, and metaphysical collecting. Historically used for sharp tools and arrowheads.
Geological facts
Despite looking like a rock, mahogany obsidian is technically a volcanic glass because it lacks a crystalline structure. The 'mahogany' patterns are often unique to each stone, representing flow bands of iron-rich impurities.
Field identification & locations
Identify by its glass-like feel, smooth conchoidal (shell-like) fracture edges, and distinctive reddish-brown and black mottling. Frequently found in volcanic regions of the Western USA (Oregon, California, Utah) and Mexico.
