igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5–5.5 Mohs scale; Color: Black to dark brown/grey (translucent at edges); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.
- Hardness
- 5–5
- Color
- Black to dark brown/grey (translucent at edges)
- Luster
- Vitreous/Glassy
Identified More igneous →
Explore Obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5–5.5 Mohs scale; Color: Black to dark brown/grey (translucent at edges); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.
Formation & geological history
Formed through the rapid cooling of silica-rich (felsic) lava, which prevents crystal growth. Usually found in geologically recent volcanic fields or areas with high rhyolitic volcanic activity.
Uses & applications
Used historically for sharp tools and weapons (scalpels, arrowheads). Modern uses include ornamental carvings, jewelry, and high-quality surgical blades.
Geological facts
Obsidian was so highly valued by ancient civilizations that it was traded over thousands of miles. It can produce a cutting edge many times sharper than premium steel surgical scalpels.
Field identification & locations
Identify in the field by its characteristic smooth, curved (conchoidal) glass-like fracture and extremely sharp edges. Commonly found in Oregon (USA), Mexico, and Iceland.
