igneous
Obsidian (likely snowflake or smoky obsidian fragment)
Volcanic glass; predominantly rhyolitic silica glass (SiO₂-rich)
AI-generated identification · may be incorrectTypically black to brown, vitreous/glassy luster, conchoidal fracture, no visible crystals or cleavage; Mohs hardness about 5–5.5, specific gravity 2.3–2.6. The specimen appears dark, translucent at edges, and possibly weathered or polished.
Identified More igneous →
Explore Obsidian (likely snowflake or smoky obsidian fragment) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically black to brown, vitreous/glassy luster, conchoidal fracture, no visible crystals or cleavage; Mohs hardness about 5–5.5, specific gravity 2.3–2.6. The specimen appears dark, translucent at edges, and possibly weathered or polished.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot grow, usually in young volcanic flows, domes, and lava margins. Commonly Quaternary to recent, though older obsidian also occurs.
Uses & applications
Used historically for exceptionally sharp blades and arrowheads; today it is collected, carved, polished, and occasionally used in jewelry or ornamental objects.
Geological facts
Fresh fracture edges can be sharper than surgical steel, although obsidian is brittle. Brown or smoky coloration commonly results from iron-bearing impurities or microscopic inclusions.
Field identification & locations
Identify it by glassy luster, sharp curved fracture surfaces, lack of crystal grains, and translucency along thin edges; a steel point may scratch it slightly. Common sources include Mexico, the western United States, Iceland, Armenia, and Japan.
