igneous
Obsidian
Volcanic Glass
Hardness of 5 to 5.5 on the Mohs scale, typically black to dark brown in color, vitreous luster, conchoidal fracture, and amorphous crystal structure.
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Physical properties
Hardness of 5 to 5.5 on the Mohs scale, typically black to dark brown in color, vitreous luster, conchoidal fracture, and amorphous crystal structure.
Formation & geological history
Formed as extrusive igneous rock when felsic lava extruded from a volcanic vent cools rapidly with minimal crystal growth.
Uses & applications
Historically used to manufacture cutting tools, arrowheads, and blades; currently used in surgical scalpel blades and jewelry.
Geological facts
Because it contains no crystal structure, obsidian breaks with extremely sharp edges, often forming fragments thinner than the wavelength of visible light.
Field identification & locations
Can be identified in the field by its dark color, glassy texture, and distinct conchoidal fracture pattern. Found worldwide in areas with past volcanic activity.
