igneous
Tumbled mahogany obsidian
Obsidian, volcanic glass (composition typically rhyolitic)
AI-generated identification · may be incorrectGlossy red-orange and black mottling; no visible crystals or cleavage. Hardness about 5–5.5 Mohs; conchoidal fracture when broken; specific gravity roughly 2.3–2.6.
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Physical properties
Glossy red-orange and black mottling; no visible crystals or cleavage. Hardness about 5–5.5 Mohs; conchoidal fracture when broken; specific gravity roughly 2.3–2.6.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot grow. It is geologically young volcanic glass, commonly associated with Quaternary eruptions.
Uses & applications
Used for beads, cabochons, carvings, and decorative objects; historically, sharp obsidian was fashioned into cutting tools.
Geological facts
The specimen appears polished and tumbled; its red-brown patches likely reflect iron-rich material or inclusions within the glass.
Field identification & locations
Mahogany obsidian is found in volcanic regions, notably the western United States and Mexico. Its glassy luster, mottled mahogany-and-black colors, and lack of crystal grains help distinguish it from crystalline rocks.
