sedimentary

Chert (specifically Flint or Gray Chert)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray, tan, or white with waxy/dull luster; Crystal Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray, tan, or white with waxy/dull luster

Identified March 17, 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. Most specimens date from the Phanerozoic eon.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to sharp edges; currently used as road aggregate, in glass manufacturing, and as a component in ceramics.

Geological facts

Chert produces sparks when struck against steel, leading to its historical use in flintlock firearms. It is one of the most durable sedimentary rocks, often remaining long after the surrounding limestone has weathered away.

Field identification & locations

Identify in the field by its conchoidal (shell-like) fracture, sharp edges, and inability to be scratched by a steel knife. Common in limestone outcrops, riverbeds, and glacial till throughout North America and Europe.