sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale. Color: Tan, beige, grey, and brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 7 Mohs scale
Color: Tan, beige, grey, and brown
Luster: Waxy to dull

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale. Color: Tan, beige, grey, and brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & geological history

Formed by the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through chemical precipitation from groundwater within limestone or chalk beds. Often found in Phanerozoic sedimentary sequences.

Uses & applications

Historically used for stone tools and starting fires. Modernly used as road aggregate, architectural stone, and sometimes in jewelry (as jasper or agate variants).

Geological facts

Chert has been used by humans for millions of years to create arrowheads and scrapers because it breaks with sharp, glass-like edges. It is chemically very stable and resistant to weathering.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, curved conchoidal fractures. Commonly found in stream beds or as nodules within limestone outcrops.