igneous
Obsidian (likely snowflake or volcanic-glass variety)
Volcanic glass, predominantly rhyolitic in composition; mainly SiO₂ with minor Al, Na, K, Fe, and Ca
AI-generated identification · may be incorrectHardness about 5–5.5 Mohs; black to dark gray, vitreous luster, amorphous glassy structure, and no cleavage. The bright curved surfaces and sharp conchoidal fractures are characteristic, while pale patches may be feldspar or devitrification.
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Physical properties
Hardness about 5–5.5 Mohs; black to dark gray, vitreous luster, amorphous glassy structure, and no cleavage. The bright curved surfaces and sharp conchoidal fractures are characteristic, while pale patches may be feldspar or devitrification.
Formation & geological history
Forms when silica-rich lava cools extremely rapidly, preventing crystal growth; most examples are Quaternary to younger, though obsidian occurs in volcanic terrains of many ages.
Uses & applications
Used for ornamental objects, cabochons, carvings, tools, and historically extremely sharp blades; also collected as a decorative volcanic rock.
Geological facts
Obsidian fractures into exceptionally sharp edges and can resemble black glass, but natural surfaces often show flow banding, bubbles, or devitrified patches.
Field identification & locations
Identify by its glassy luster, conchoidal fracture, lack of visible crystals, and moderate density; common localities include Mexico, the western United States, Iceland, Armenia, and Japan. The specimen appears natural and rough, though exact variety requires closer inspection.
