igneous
Obsidian
Obsidian (Volcanic Glass, SiO2 + impurities)
Hardness: 5-5.5 on Mohs scale. Color: Black (shown), also green, brown, or gold sheen. Luster: Vitreous/Glassy. Structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.35-2.6.
- Hardness
- 5-5
- Color
- Black (shown), also green, brown, or gold sheen
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5 on Mohs scale. Color: Black (shown), also green, brown, or gold sheen. Luster: Vitreous/Glassy. Structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.35-2.6.
Formation & geological history
Formed from rapid cooling of felsic (silica-rich) lava, preventing crystal growth. It is found in geologically young areas due to its tendency to devitrify over time.
Uses & applications
Used in surgical scalpel blades for extreme sharpness, ornamental jewelry (cabochons and beads), construction as a raw material for rock wool, and highly valued by lapidary collectors.
Geological facts
Ancient cultures used obsidian for projectile points and mirrors. It is technically a 'mineraloid' rather than a mineral because it lacks a crystalline structure. It is essentially frozen liquid.
Field identification & locations
Identify in the field by its characteristic conchoidal fracture (curved, shell-like breaks) and sharp edges. Commonly found in volcanic regions like the American West (Oregon, California), Mexico, and Iceland.
