igneous
Obsidian
Volcanic Glass (predominantly SiO2)
Hardness: 5-5.5 Mohs; Color: Jet black; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Jet black
- Luster
- Vitreous (glassy)
Identified More igneous →
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Physical properties
Hardness: 5-5.5 Mohs; Color: Jet black; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific Gravity: 2.35-2.6
Formation & geological history
Formed through the rapid cooling of felsic (silica-rich) lava, which prevents the growth of mineral crystals. It is typically found in volcanic regions from the Quaternary period.
Uses & applications
Used historically for arrowheads and cutting tools; currently used for surgical scalpel blades, jewelry, decorative ornaments, and gemstone therapy.
Geological facts
Obsidian fractures with extremely sharp edges—to a molecular level—making its blades sharper than high-quality steel scalpels. It is technically 'frozen liquid' rather than a true mineral.
Field identification & locations
Identify by its glass-like texture and curved, shell-like (conchoidal) fractures. Found in volcanic areas like the American West (Glass Buttes), Mexico, and Iceland.
