igneous
Black Obsidian
Amorphous volcanic glass (SiO2)
Hardness: 5 to 6; Color: Deep black; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35 to 2.6
- Hardness
- 5 to 6
- Color
- Deep black
- Luster
- Vitreous/glassy
Identified More igneous →
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Physical properties
Hardness: 5 to 6; Color: Deep black; Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35 to 2.6
Formation & geological history
Forms when felsic lava (rich in silica) cools so rapidly that there is no time for crystals to grow. Usually associated with geologically recent volcanic activity.
Uses & applications
Used in ornamental jewelry, decorative sculptures, and historically as sharp blades or arrowheads. In modern medicine, it is occasionally used for high-precision surgical scalpels.
Geological facts
Obsidian is technically not a mineral because it doesn't have a crystal structure; it is often called a mineraloid. It breaks with extremely sharp edges that can be much sharper than a surgical steel blade.
Field identification & locations
Identify by its smooth, glassy texture and distinctive shell-like (conchoidal) fractures. Found in areas of recent volcanic activity such as Iceland, Mexico, or the Western US.
