sedimentary
Chert
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Gray, green, brown, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, green, brown, tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, green, brown, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the recrystallization of silica-rich microfossils (like radiolarians or diatoms) on the seafloor, or via chemical precipitation from hydrothermal fluids. Commonly found in limestone or dolostone layers.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Today used as road base, construction aggregate, and occasionally for lapidary work.
Geological facts
Chert is so hard it can strike sparks against steel. This specific specimen shows 'knapping' features similar to a lithic flake or debitage, suggesting it may have been historically worked by humans.
Field identification & locations
Identify by its waxy texture, hardness (it will scratch glass), and its characteristic shell-like (conchoidal) curved fracture surfaces. Found worldwide in sedimentary basins.
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