igneous
Black Obsidian
Volcanic glass (Amorphous silicates)
Hardness: 5 to 5.5 on the Mohs scale; Color: Deep black, sometimes translucent; Luster: Vitreous (glassy); Crystal structure: Amorphous (no true crystal lattice); Cleavage: Conchoidal fracture, producing extremely sharp edges; Specific gravity: 2.35 to 2.6.
- Hardness
- 5 to 5
- Color
- Deep black, sometimes translucent
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5 to 5.5 on the Mohs scale; Color: Deep black, sometimes translucent; Luster: Vitreous (glassy); Crystal structure: Amorphous (no true crystal lattice); Cleavage: Conchoidal fracture, producing extremely sharp edges; Specific gravity: 2.35 to 2.6.
Formation & geological history
Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found worldwide near recent volcanic activity.
Uses & applications
Used historically for sharp cutting tools, arrowheads, and blades, as well as in modern decorative items, jewelry, and metaphysical healing practices.
Geological facts
Because obsidian cools so rapidly that crystals do not have time to grow, it is technically a mineraloid rather than a true mineral. Its conchoidal fracture allows it to be chipped into edges significantly sharper than high-quality surgical steel.
Field identification & locations
Easily identified by its deep black color, glassy luster, and characteristic conchoidal fracture. Common in volcanic regions globally and entirely plausible to find as a tumbled specimen in California due to regional trade and volcanic history.
