igneous
Black Obsidian cabochon
Volcanic Glass (SiO2 + impurities)
Mohs Hardness: 5-5.5; Color: Deep black with some translucency; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6.
- Hardness
- 5-5
- Color
- Deep black with some translucency
- Luster
- Vitreous/Glassy
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Physical properties
Mohs Hardness: 5-5.5; Color: Deep black with some translucency; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35-2.6.
Formation & geological history
Formed by the extremely rapid cooling of silica-rich (rhyolitic) lava, preventing crystal growth. Usually found in volcanic regions from the Tertiary and Quaternary periods.
Uses & applications
Historically used for sharp tools and weapons. Currently used for jewelry, scalpels, decorative figurines, and metaphysical collecting.
Geological facts
Obsidian is technically a glass, not a mineral, because it lacks a crystalline structure. It is one of the sharpest materials known, able to create blades thinner than high-quality steel.
Field identification & locations
Identified by its smooth, glassy surface and razor-sharp conchoidal (shell-like) fracture edges. Commonly found in Oregon, Mexico, and Greece. Collectors look for unique optical effects like gold or rainbow sheen.
