igneous
Obsidian (likely snowflake or banded variety)
Volcanic glass, primarily SiO₂
AI-generated identification · may be incorrectUsually black to dark brown with vitreous luster, conchoidal fracture, and no visible crystals; Mohs hardness about 5–5.5, poor cleavage, specific gravity approximately 2.35–2.70. The specimen appears rough, glossy, and fractured, consistent with obsidian, though image identification is limited.
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Physical properties
Usually black to dark brown with vitreous luster, conchoidal fracture, and no visible crystals; Mohs hardness about 5–5.5, poor cleavage, specific gravity approximately 2.35–2.70. The specimen appears rough, glossy, and fractured, consistent with obsidian, though image identification is limited.
Formation & geological history
Rapid cooling of silica-rich volcanic lava prevented crystal growth, producing natural glass, commonly during Quaternary volcanic eruptions. It forms in rhyolitic lava flows, domes, and margins of volcanic vents.
Uses & applications
Used historically for exceptionally sharp tools and arrowheads; today it is collected, carved, used for ornamental objects, and occasionally made into jewelry. It has little value unless unusually clear, patterned, or well-polished.
Geological facts
Fresh edges can be sharper than surgical steel, but obsidian is brittle and breaks readily. Weathering may produce a dull surface or hydration rind.
Field identification & locations
Identify by its glassy luster, sharp conchoidal edges, lack of grains, and black/brown color; distinguish it from glass by natural flow banding, vesicles, or a rough weathered rind. Common localities include Mexico, the western United States, Armenia, and Iceland.
