igneous
Obsidian
Volcanic glass
Hardness: 5-5.5 (Mohs scale), Color: Jet black (sometimes grey or brown), Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.4
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs scale), Color: Jet black (sometimes grey or brown), Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.4
Formation & geological history
Formed through the rapid cooling of silica-rich felsic lava, which prevents crystal growth. Usually found in volcanic regions from the Pliocene to Holocene eras.
Uses & applications
Historically used for making sharp tools/weapons (arrowheads); currently used for decorative jewelry, surgical scalpel blades, and metaphysical collecting.
Geological facts
Because it is glass and not a mineral, it has no internal crystal structure. It breaks with extremely sharp edges—thinner than surgical steel—making it useful for specialized medical procedures.
Field identification & locations
Identify by its glass-like appearance, conchoidal (shell-like) fracture patterns, and sharp edges. Commonly found in Oregon, California, Iceland, and Mexico.
