igneous
Tumbled mahogany obsidian
Volcanic glass; primarily SiO₂ with iron-oxide-rich brown inclusions
AI-generated identification · may be incorrectHardness about 5–5.5 Mohs; dark brown to black, vitreous luster, smooth conchoidal fracture, amorphous (non-crystalline), and no cleavage. The rounded shape indicates tumbling and polishing.
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Physical properties
Hardness about 5–5.5 Mohs; dark brown to black, vitreous luster, smooth conchoidal fracture, amorphous (non-crystalline), and no cleavage. The rounded shape indicates tumbling and polishing.
Formation & geological history
Rapid cooling of silica-rich rhyolitic lava produced natural volcanic glass; reddish-brown areas reflect iron-oxide inclusions or flow banding. Most examples are Quaternary to Recent, commonly from volcanic regions of the western United States and Mexico.
Uses & applications
Used for cabochons, beads, carvings, ornaments, and lapidary collections; historically, obsidian was knapped into extremely sharp tools and arrowheads.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks an ordered crystal lattice. Mahogany obsidian’s brown-red pattern distinguishes it from uniformly black obsidian.
Field identification & locations
Identify by its glassy appearance, rounded conchoidal textures, and inability to show visible crystals; it is much softer than quartz. Common sources include Oregon, Utah, Arizona, California, and Mexico.
