sedimentary
Chert (varietal Flint)
Chert (SiO2)
Hardness: 7 Mohs; Color: Gray, white, or beige; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Gray, white, or beige
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Gray, white, or beige; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed by the precipitation of microcrystalline silica from water, often replacing organic material or filling cavities in limestone/chalk. Found in formations from the Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used as a road aggregate, in glass making, and as decorative gravel.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. It was the most important material for early human tool development because of how it breaks into sharp edges.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture and ability to scratch glass. Commonly found as nodules in riverbeds or limestone outcroppings.
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