sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Grey, brown, yellowish, or tan with waxy/dull luster; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Grey, brown, yellowish, or tan with waxy/dull luster

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often Paleozoic to Mesozoic in age.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used as road aggregate, in glass manufacturing, and as a starting material for sparking (fire-making).

Geological facts

Chert is so hard it can scratch steel. When struck against iron or steel, it produces sparks due to its hardness and friction, making it a primary tool for survivalist fire-starting.

Field identification & locations

Identify by its waxy appearance, extreme hardness, and 'shell-like' conchoidal fractures. Commonly found in stream beds or weathered out of carbonate rock outcrops globally. Collectors look for colorful variants like jasper or agate.