igneous
Black Obsidian with white veins
Volcanic Glass (70–75% SiO2)
Hardness: 5–6 Mohs; Color: Jet black with thin white streaks or inclusions; Luster: Vitreous (glass-like); Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35–2.6.
- Hardness
- 5–6 Mohs
- Color
- Jet black with thin white streaks or inclusions
- Luster
- Vitreous (glass-like)
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Physical properties
Hardness: 5–6 Mohs; Color: Jet black with thin white streaks or inclusions; Luster: Vitreous (glass-like); Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35–2.6.
Formation & geological history
Formed when high-silica lava cools too quickly for crystals to grow. The white veins are typically caused by trace amounts of internal stressors during cooling or inclusions of minerals like feldspar or quartz filling cracks.
Uses & applications
Commonly used for gemstone jewelry, decorative carvings, and scalpel blades (due to its ability to be fractured to a molecularly thin edge). Also popular in metaphysical collections.
Geological facts
Obsidian is technically a supercooled liquid, not a mineral, because it lacks a crystalline structure. Ancient civilizations throughout the Americas and Mediterranean used it for tools and projectile points.
Field identification & locations
Identify in the field by its characteristic smooth, curved (conchoidal) fractures and glass-like texture. Frequently found near geologically recent volcanic sites such as Oregon, Mexico, or Iceland. Collectors should look for its sharp edges.
