igneous
Black Obsidian
Obsidian (Volcanic Glass, SiO2 + impurity)
Hardness: 5-5.5 | Color: Jet black, opaque to translucent at edges | Luster: Vitreous/Glassy | Structure: Amorphous (non-crystalline) | Fracture: Conchoidal | Specific Gravity: 2.4
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 | Color: Jet black, opaque to translucent at edges | Luster: Vitreous/Glassy | Structure: Amorphous (non-crystalline) | Fracture: Conchoidal | Specific Gravity: 2.4
Formation & geological history
Formed by the rapid cooling of silica-rich (felsic) lava, preventing the formation of crystals. Most commonly associated with volcanic activity from the Pliocene to the Holocene epochs.
Uses & applications
Historically used for blades and arrowheads; currently used in jewelry (beads, cabochons), modern surgical scalpels, and as decorative tumbled stones.
Geological facts
Obsidian is technically not a mineral because it is amorphous (lacks a crystal structure); it is a mineraloid. It breaks with extremely sharp edges—thinner and sharper than a steel scalpel.
Field identification & locations
Identified by its jet-black color, glassy surface, and shell-like (conchoidal) fracture pattern. Tumbled specimens feel smooth and are relatively light for their size. Commonly found in volcanic areas like Oregon, Mexico, and Iceland.
