igneous
Obsidian
Obsidian (Volcanic Glass, SiO2 dominated)
Hardness: 5.0–6.0; Color: Black, dark brown, or grey; Luster: Vitreous (glassy); Crystal Structure: Amorphous; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6; Features: Sharp edges and smooth, curved surfaces when broken.
- Hardness
- 5
- Color
- Black, dark brown, or grey
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5.0–6.0; Color: Black, dark brown, or grey; Luster: Vitreous (glassy); Crystal Structure: Amorphous; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6; Features: Sharp edges and smooth, curved surfaces when broken.
Formation & geological history
Formed from the rapid cooling of silica-rich felsic lava, which prevents crystal growth. It is found in geologically recent volcanic fields or areas with rhyolitic activity.
Uses & applications
Historically used for arrowheads and blades; currently used for surgical scalpels, decorative gemstones, jewelry, and metaphysical collecting.
Geological facts
Obsidian is technically a glass rather than a true mineral because it lacks a crystalline structure. Native American tribes traded obsidian across vast distances for tool making.
Field identification & locations
Identify in the field by its distinctive glassy appearance and conchoidal (shell-like) fracture patterns. Commonly found in Oregon, California, Iceland, and Mexico. Collectors look for unique variations like snowflake, mahogany, or rainbow obsidian.
