sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and grey (likely jasperoid chert); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and grey (likely jasperoid chert)
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and grey (likely jasperoid chert); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica in sedimentary environments, often replacing carbonate materials in limestone or accumulating from the remains of silica-shelled organisms like dioramas or radiolaria.
Uses & applications
Historically used for making stone tools (arrowheads). Modern uses include construction aggregate, gemstones (when colorful), and fire-starting kits (flint-on-steel).
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the first materials traded globally by prehistoric humans due to its ability to hold a sharp edge.
Field identification & locations
Identify by its conchoidal fracture (curved, shell-like breaks) and waxy texture. It is extremely common in gravel pits, riverbeds, and limestone outcrops worldwide.
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