igneous
Polished mahogany obsidian (likely)
Volcanic glass; primarily silica-rich rhyolitic glass (SiO₂), with iron oxides
AI-generated identification · may be incorrectHardness about 5–5.5 Mohs; dark reddish-brown to black, vitreous luster, smooth conchoidal fracture, and no visible crystals or cleavage. The rounded shape indicates tumbling or polishing, and the pale area may be reflected light or a natural flow-band variation.
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Physical properties
Hardness about 5–5.5 Mohs; dark reddish-brown to black, vitreous luster, smooth conchoidal fracture, and no visible crystals or cleavage. The rounded shape indicates tumbling or polishing, and the pale area may be reflected light or a natural flow-band variation.
Formation & geological history
Forms when viscous, silica-rich lava cools so rapidly that crystals cannot develop, commonly during Quaternary volcanic eruptions. Mahogany coloration results from dispersed iron-oxide inclusions.
Uses & applications
Used for cabochons, beads, carvings, ornaments, and lapidary specimens; rarely used as a functional industrial material.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks an ordered crystal lattice. Its sharp conchoidal edges were historically used for cutting tools and arrowheads.
Field identification & locations
Identify by its glassy surface, conchoidal fracture, lack of grain, and red-brown/black coloration; common sources include Mexico, the western United States, Armenia, and Turkey. The image alone cannot exclude polished jasper or other dark volcanic glass.
