sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

Identified February 26, 2026More sedimentary →

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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.