igneous
Black Obsidian
Volcanic Glass (SiO2 with impurities)
Mohs hardness 5.0 to 5.5. Color is deep jet black to dark brown. Vitreous (glassy) luster with distinct conchoidal fracture and sharp edges. Amorphous crystal structure (non-crystalline).
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Physical properties
Mohs hardness 5.0 to 5.5. Color is deep jet black to dark brown. Vitreous (glassy) luster with distinct conchoidal fracture and sharp edges. Amorphous crystal structure (non-crystalline).
Formation & geological history
Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in volcanic environments worldwide.
Uses & applications
Historically used for stone tools, arrowheads, and blades. Modern uses include surgical scalpel blades, gemstone carvings, cabochons, and decorative mineral specimens.
Geological facts
Obsidian fractures into extremely sharp edges—sharp enough to be used in delicate surgical procedures where a finer cut than steel is required.
Field identification & locations
Identified by its shiny, glassy appearance, jet-black color, and smooth curved conchoidal fractures. Commonly found in volcanic areas such as the western United States, Mexico, and Iceland.
