sedimentary

Chert

Sedimentary Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically earthy browns, tans, or grays; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: typically earthy browns, tans, or grays
Luster: waxy to dull

Identified June 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. Commonly found in Paleozoic and Mesozoic strata.

Uses & applications

Historically used for making stone tools (arrowheads and scrapers) due to its sharp edges; used today as a construction aggregate and occasionally as a flint for fire-starting.

Geological facts

Chert is so hard it can scratch steel and glass. In its darker, more lustrous form, it is known as flint. It has been used by humans for over 2 million years.

Field identification & locations

Identify by its 'conchoidal' (shell-like) fracture pattern and its inability to be scratched by a steel knife. Commonly found as nodules or layers within limestone outcrops.