igneous
Sheen Obsidian
Volcanic glass (SiO2 with inclusions)
Hardness: 5-5.5 (Mohs scale); Color: Black with golden or brown sheen; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Black with golden or brown sheen
- Luster
- Vitreous/Glassy
Identified More igneous →
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Physical properties
Hardness: 5-5.5 (Mohs scale); Color: Black with golden or brown sheen; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6
Formation & geological history
Formed through the rapid cooling of silica-rich felsic lava. The sheen effect is caused by tiny bubbles of gas or microscopic mineral inclusions trapped in the glass as it solidified.
Uses & applications
Used primarily for jewelry (cabochons), ornamental carvings, and by collectors. Historically used for making razor-sharp tools and weapons.
Geological facts
Obsidian is often called 'nature's glass'. The gold or mahogany sheen variants are a result of specific impurities or gas bubbles aligned along flow layers of the lava.
Field identification & locations
Identify by its glass-like texture, sharp edges if broken, and the way the color shifts when turned in the light. Commonly found in volcanic regions of Mexico and the American West.
