sedimentary

Chert

Chert (SiO2)

Hardness: 7 Mohs scale; Color: typically white, tan, or gray with waxy or dull luster; Structure: Cryptocrystalline Quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: typically white, tan, or gray with waxy or dull luster

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: typically white, tan, or gray with waxy or dull luster; Structure: Cryptocrystalline Quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of siliceous remains of microscopic organisms like diatoms or radiolarians, or through chemical precipitation from silica-rich fluids in limestone/dolomite cavities. Common in Phanerozoic sedimentary sequences.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges and hardness. Today used in construction aggregate and as a collector's specimen.

Geological facts

Chert has a conchoidal fracture which means it breaks like glass, producing very sharp edges. In its black form, it is often called flint, which was vital for starting fires in antiquity.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found as nodules or layers within limestone beds.