sedimentary

Chert (Flint Pebbles)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, black, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 7 on Mohs scale
Color: Gray, black, or tan
Luster: Waxy to dull

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, black, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed as nodules in limestone or chalk through the accumulation of silica-rich organic remains (like sponges or diatoms) or chemical precipitation. Primarily found in Phanerozoic era strata.

Uses & applications

Historically used for making stone tools and starting fires; currently used as construction aggregate, road surfacing, and occasionally as a semi-precious gemstone.

Geological facts

Chert is so hard it cannot be scratched by a steel knife. It was one of the first minerals extensively traded by early humans for tool and weapon production.

Field identification & locations

Identify in the field by its smooth, waxy feel and distinct shell-like (conchoidal) fractures. Often found in riverbeds or weathered out of carbonate rock formations.