igneous
Obsidian
Amorphous volcanic glass (primarily SiO2)
Hardness: 5 to 6; Color: black to dark brown; Luster: vitreous; Crystal Structure: amorphous (none); Cleavage: none, exhibits conchoidal fracture; Specific Gravity: 2.35 to 2.6
- Hardness
- 5 to 6
- Color
- black to dark brown
- Luster
- vitreous
Identified More igneous →
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Physical properties
Hardness: 5 to 6; Color: black to dark brown; Luster: vitreous; Crystal Structure: amorphous (none); Cleavage: none, exhibits conchoidal fracture; Specific Gravity: 2.35 to 2.6
Formation & geological history
Extrusive igneous rock formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in geologically recent volcanic areas.
Uses & applications
Historically used for making sharp tools and weapons. Today used for surgical scalpel blades, jewelry, and ornamental art.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it is non-crystalline; it is also known for producing the sharpest edges in existence, down to molecular thickness.
Field identification & locations
Identify by its glass-like texture, sharp edges, and distinctive conchoidal (shell-like) fractures. Common in Western US, Iceland, and Mexico. Collectors look for unique varieties like snowflake or mahogany obsidian.
