igneous
Obsidian
Volcanic glass (SiO2 - Silicon Dioxide with impurities)
Hardness: 5–5.5; Color: Jet black (can be dark green or brown); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4
- Hardness
- 5–5
- Color
- Jet black (can be dark green or brown)
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5–5.5; Color: Jet black (can be dark green or brown); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4
Formation & geological history
Formed from the rapid cooling of silica-rich (felsic) lava, which prevents crystal growth. It is primarily found in Cenozoic era volcanic regions.
Uses & applications
Historically used for arrowheads and blades; modernly used for high-end surgical scalpels, decorative ornaments, gemstone jewelry, and metaphysical collecting.
Geological facts
Because it is a glass and not a true mineral, it is technically a 'mineraloid.' It produces a cutting edge many times sharper than high-quality steel scalpels.
Field identification & locations
Identify by its characteristic shell-like (conchoidal) fracture lines and extremely sharp edges. Commonly found in volcanic fields such as those in Iceland, Mexico, or the Western USA.
