igneous
Obsidian
Volcanic Glass
AI-generated identification · may be incorrectMohs hardness 5 to 5.5, jet black color, vitreous luster, amorphous crystal structure, conchoidal fracture, specific gravity 2.35 to 2.45.
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Physical properties
Mohs hardness 5 to 5.5, jet black color, vitreous luster, amorphous crystal structure, conchoidal fracture, specific gravity 2.35 to 2.45.
Formation & geological history
Formed as an extrusive igneous rock when felsic lava cools rapidly with minimal crystal growth, typically in volcanic environments.
Uses & applications
Used historically for sharp cutting tools and arrowheads, and currently in decorative objects, jewelry, and occasional surgical scalpel blades.
Geological facts
Because it lacks a crystalline structure, it breaks with exceptionally sharp edges that can be finer than surgical steel.
Field identification & locations
Identified by its glossy black appearance, glass-like texture, and distinct conchoidal fracture patterns; found globally near recent volcanic activity.
