igneous
Red obsidian (likely mahogany obsidian)
Volcanic glass; primarily silica-rich rhyolitic glass (SiO₂), commonly with iron-oxide inclusions
AI-generated identification · may be incorrectHardness about 5–5.5 Mohs; deep wine-red to brown with black areas, vitreous luster, and no crystal structure or cleavage. It fractures conchoidally, producing very sharp edges; the rough surface appears natural rather than polished.
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Physical properties
Hardness about 5–5.5 Mohs; deep wine-red to brown with black areas, vitreous luster, and no crystal structure or cleavage. It fractures conchoidally, producing very sharp edges; the rough surface appears natural rather than polished.
Formation & geological history
Rapid cooling of silica-rich lava formed this amorphous volcanic glass, generally during Quaternary volcanic activity. Red coloration typically comes from dispersed hematite or other iron oxides, while darker zones reflect less oxidized material.
Uses & applications
Used for decorative objects, lapidary carvings, cabochons, and historically for blades and tools. Attractive, translucent, sharply fractured pieces have modest collector appeal.
Geological facts
Obsidian is not technically a mineral because it lacks an ordered crystal lattice. Its glassy fracture can resemble flint, but its smooth curved fracture surfaces and volcanic context are characteristic.
Field identification & locations
Identify it by glassy luster, conchoidal fracture, lack of visible grains, and sharp edges; a scratch test should place it near window glass. Common sources include Oregon, Utah, Arizona, Mexico, Armenia, and Japan.
