sedimentary

Chert (Flint)

Chert (Cryptocrystalline variety of Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brown, gray, and cream with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, brown, gray, and cream with waxy luster

Identified March 14, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, gray, and cream with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids. Generally found in marine limestone or dolomite beds as nodules or layers. Can range from Precambrian to Recent geological periods.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Modernly used in road construction, as a source for silica in glassmaking, and by survivalists for fire-starting.

Geological facts

Because of its conchoidal fracture, it can be knapped to create edges sharper than a steel scalpel. Native Americans and many ancient cultures traded high-quality chert over thousands of miles.

Field identification & locations

Identify in the field by its very hard, smooth surface that cannot be scratched by steel and its sharp, shell-like (conchoidal) breaks. Often found as hard nodules protruding from softer limestone cliffs.