sedimentary

Chert (Sedimentary Rock)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Tan, beige, or grey with waxy/dull luster; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 7 (Mohs scale)
Color: Tan, beige, or grey with waxy/dull luster

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, beige, or grey with waxy/dull luster; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; commonly found in limestone or dolostone formations.

Uses & applications

Historically used for making stone tools (flintknapping); currently used as road aggregate, in landscaping, and as a raw material for silicon-based products.

Geological facts

Chert is extremely durable and chemically stable. Varieties include flint, jasper, and agate. It was one of the most important minerals for early humans due to its ability to break with sharp edges.

Field identification & locations

Identify by its waxy texture, ability to scratch glass, and rounded, shell-like (conchoidal) fracture patterns. Frequently found in creek beds and as nodules within sedimentary layers.