igneous
Mahogany Obsidian
Volcanic glass (SiO2 with Hematite or Magnetite inclusions)
Hardness: 5-5.5 (Mohs), Color: Black with reddish-brown streaks/patches, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Specific Gravity: 2.35-2.6
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs), Color: Black with reddish-brown streaks/patches, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Specific Gravity: 2.35-2.6
Formation & geological history
Formed from rapidly cooling felsic lava where crystallization cannot occur. The mahogany coloration comes from inclusions of Magnetite or Hematite (iron oxide) occurring during the cooling process.
Uses & applications
Used for making jewelry, ornamental carvings, knife blades (scalpels), and by collectors as a decorative stone.
Geological facts
Obsidian fractures with extremely sharp edges, known as conchoidal fracture. In some cases, it can be honed to an edge much thinner and sharper than high-quality steel surgical scalpels.
Field identification & locations
Identify by its glass-like texture, reddish-brown and black swirling patterns, and sharp edges if broken. Commonly found in volcanic regions of the USA (Oregon, California), Mexico, and Japan.
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