igneous
Silver Sheen Obsidian
Volcanic Glass (Amorphous Silicon Dioxide - SiO2 with impurities)
Hardness: 5–5.5 on Mohs scale. Color: Black with a silvery metallic chatoyancy (sheen) when turned in light. Luster: Vitreous/Glassy. Structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.35–2.6.
- Hardness
- 5–5
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5–5.5 on Mohs scale. Color: Black with a silvery metallic chatoyancy (sheen) when turned in light. 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. The silver sheen is caused by tiny bubbles of gas or microscopic inclusions of water vapor or minerals (like feldspar) trapped in the glass during cooling.
Uses & applications
Used primarily in jewelry (beads, cabochons), ornamental carvings, and metaphysical collecting. Historically used for making razor-sharp tools and weapons.
Geological facts
Obsidian is technically a glass rather than a mineral because it lacks a crystalline structure. The 'sheen' effect is a type of chatoyancy caused by light reflecting off internal gas bubbles. It has been used for thousands of years for mirrors and ritual objects.
Field identification & locations
Identify by looking for a black glassy surface that reveals a silvery 'flash' when tilted under direct light. Commonly found in volcanic regions like Mexico, the United States (Oregon/California), and Iceland.
