igneous
Obsidian (likely snowflake or sheen obsidian)
Volcanic glass, predominantly silica-rich rhyolitic composition (approximately 70–75% SiO₂)
AI-generated identification · may be incorrectBlack, vitreous to glassy luster with conchoidal fracture and sharp edges; hardness about 5–5.5 Mohs, amorphous rather than crystalline, and typically no cleavage. The blue-white reflective patch suggests sheen obsidian or surface polish.
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Physical properties
Black, vitreous to glassy luster with conchoidal fracture and sharp edges; hardness about 5–5.5 Mohs, amorphous rather than crystalline, and typically no cleavage. The blue-white reflective patch suggests sheen obsidian or surface polish.
Formation & geological history
Forms when silica-rich lava cools extremely rapidly, preventing crystal growth; commonly Quaternary to younger in volcanic regions. The metallic-looking adjacent fragment may be an inclusion or a separate mineral specimen.
Uses & applications
Used for ornamental objects, cabochons, arrowheads, blades, and jewelry; exceptionally sharp edges have limited surgical and experimental use. Common specimens generally have modest collector value.
Geological facts
Obsidian is technically volcanic glass, not a conventional crystalline mineral. Hydration-rim dating can sometimes estimate its geological age, while its conchoidal fracture is diagnostic.
Field identification & locations
Identify by black glassy appearance, sharp curved fracture, and lack of visible crystals; blue or golden sheen appears when light reflects from microscopic inclusions or flow layers. Common localities include Mexico, the western United States, Armenia, Iceland, and Japan.
