igneous
Obsidian
Obsidian (Volcanic Glass, SiO2 + impurities)
Hardness: 5–5.5 (Mohs); Color: Black, dark brown, or green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.3–2.6.
- Hardness
- 5–5
- Color
- Black, dark brown, or green
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5–5.5 (Mohs); Color: Black, dark brown, or green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.3–2.6.
Formation & geological history
Formed from the rapid cooling of silica-rich (rhyolitic) lava, which prevents the growth of mineral crystals. It is found in geologically young volcanic regions (primarily Cenozoic era).
Uses & applications
Used in ornamental jewelry, scalpel blades for high-precision surgery, decorative figurines, and as a focus for crystal healing collections.
Geological facts
Because it is essentially liquid lava frozen in time, it lacks an internal crystal structure. Ancient Mesoamerican civilizations used it for weaponry, such as the Macuahuitl, because it can be knapped to an edge thinner than a steel razor.
Field identification & locations
Identified by its deep black color and shell-like (conchoidal) fracture pattern. It feels smooth and glass-like to the touch. Found in volcanic areas like the Western US, Mexico, and Iceland.
