igneous
Obsidian
Volcanic Glass
Hardness of 5 to 5.5 on the Mohs scale, typically black to dark brown in color, vitreous (glassy) luster, amorphous crystal structure with no true cleavage, conchoidal fracture.
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Physical properties
Hardness of 5 to 5.5 on the Mohs scale, typically black to dark brown in color, vitreous (glassy) luster, amorphous crystal structure with no true cleavage, conchoidal fracture.
Formation & geological history
Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.
Uses & applications
Used historically for sharp cutting tools, arrowheads, and blades, as well as in jewelry and ornamental objects.
Geological facts
Because it cools so quickly, atoms do not have time to form a crystalline structure, resulting in natural glass.
Field identification & locations
Easily identified by its glass-like appearance, smooth curved conchoidal fracture, and sharp edges. Found worldwide in areas with past volcanic activity.
