igneous
Polished mahogany obsidian (probable)
Volcanic glass; chiefly rhyolitic silica-rich glass (SiO₂), compositionally near rhyolite
AI-generated identification · may be incorrectDark brown to nearly black, vitreous luster, smooth domed polish, and no visible crystals or cleavage; Mohs hardness about 5–5.5, conchoidal fracture, specific gravity roughly 2.35–2. unverified. The reddish-brown color may also indicate jasper or iron-stained volcanic glass.
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Physical properties
Dark brown to nearly black, vitreous luster, smooth domed polish, and no visible crystals or cleavage; Mohs hardness about 5–5.5, conchoidal fracture, specific gravity roughly 2.35–2. unverified. The reddish-brown color may also indicate jasper or iron-stained volcanic glass.
Formation & geological history
Forms when silica-rich lava cools too quickly for crystals to grow, typically during Quaternary to older volcanic eruptions. Mahogany coloration results from iron-oxide inclusions or flow banding.
Uses & applications
Used for cabochons, beads, carvings, ornaments, and lapidary tools; not generally used as structural stone.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks an ordered crystal lattice. The specimen appears tumbled or cabochon-polished.
Field identification & locations
Common sources include Mexico, the western United States, Armenia, and Turkey. Confirm with a conchoidal edge, glassy luster, and absence of granular crystals; a hardness or streak test can distinguish it from softer dyed materials.
