igneous
Black Obsidian (Tumbled/Polished)
Obsidian (natural volcanic silica glass, ~70–75% SiO2)
AI-generated identification · may be incorrectHardness 5–5.5; pitch-black to dark brown; vitreous to sub-vitreous luster; amorphous (no crystal structure); conchoidal fracture.
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Physical properties
Hardness 5–5.5; pitch-black to dark brown; vitreous to sub-vitreous luster; amorphous (no crystal structure); conchoidal fracture.
Formation & geological history
Formed through rapid cooling of felsic, silica-rich lava which prevents mineral crystallization, commonly occurring in geologically recent volcanic fields.
Uses & applications
Popular for tumbled pocket stones, jewelry, decorative carvings, and historically used for ultra-sharp surgical blades and tools.
Geological facts
Because obsidian fractures down to molecular-level thinness, its edges can be significantly sharper than the finest steel surgical scalpels.
Field identification & locations
Identified by its jet-black glassy look, smooth polished surface, and conchoidal chipping around edges; found extensively in volcanic regions like Oregon, Mexico, and Iceland.
