sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or white
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through chemical precipitation in marine environments and limestone cavities.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modernly used in construction aggregate, road surfacing, and as a component in glass manufacturing.
Geological facts
Chert is so hard it can produce sparks when struck against steel, which made it essential for flintlock firearms and early fire-starting.
Field identification & locations
Identify in the field by its very smooth, shell-like (conchoidal) fracture surfaces and sharp edges. It is commonly found in limestone or chalk deposits globally.
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