igneous
Obsidian
Obsidian (Volcanic Glass)
Hardness: 5-5.5 (Mohs), Color: Black to dark brown, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Cleavage: None/Conchoidal fracture, SG: 2.3-2.6
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 (Mohs), Color: Black to dark brown, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Cleavage: None/Conchoidal fracture, SG: 2.3-2.6
Formation & geological history
Formed from extrusive igneous activity when felsic lava cools rapidly with minimal crystal growth. Often found in volcanic regions from the Holocene or Pleistocene epochs.
Uses & applications
Used historically for sharp tools and weapons (scalpels, arrowheads). Modern uses include jewelry, decorative sculptures, and metaphysical collecting.
Geological facts
Because it is volcanic glass, it is metastable and eventually devitrifies into quartz over millions of years. It was a primary trade commodity in ancient empires like the Maya.
Field identification & locations
Identify by its glass-like appearance and smooth, curved (conchoidal) fractures that create razor-sharp edges. Look for it near rhyolitic volcanic sites like Glass Buttes or Yellowstone.
