sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, black, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Gray, black, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, black, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed primarily through the chemical precipitation of silica-rich fluids in marine environments or by the replacement of carbonate minerals in limestone. It occurs in nodules or layered beds within sedimentary rock sequences dating from the Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modernly used as road aggegrate, decorative landscaping stone, and in ceramic manufacturing. Specialized use in fire-starting kits.
Geological facts
Flint is a variety of chert that has been prized by humans for over two million years because it breaks into sharp edges. It was a primary spark-generating stone used in flintlock firearms from the 17th to 19th centuries.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture pattern and its ability to scratch glass. It is commonly found in chalk or limestone outcrops and along stream beds. Collectors look for sharp edges and color variations.
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