igneous
Polished mahogany obsidian
Obsidian, naturally occurring volcanic glass; typically silica-rich rhyolitic composition
AI-generated identification · may be incorrectReddish-brown with dark, rounded patches and a polished luster. Hardness about 5–5.5 Mohs; amorphous (no crystal structure), with conchoidal fracture and no cleavage.
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Physical properties
Reddish-brown with dark, rounded patches and a polished luster. Hardness about 5–5.5 Mohs; amorphous (no crystal structure), with conchoidal fracture and no cleavage.
Formation & geological history
Forms when silica-rich lava cools rapidly enough to prevent crystal growth. The specimen’s exact geological age and source cannot be determined from the image.
Uses & applications
Used for lapidary carvings, beads, and decorative objects; obsidian has also been used historically for sharp tools.
Geological facts
Mahogany obsidian is a trade name for brown-and-black patterned obsidian, not a separate mineral species.
Field identification & locations
The glassy appearance, lack of visible crystals, and sharp fracture are characteristic of obsidian; common sources include volcanic regions of the western United States and Mexico. This rounded piece appears polished and shaped.
