sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown with waxy luster

Identified March 22, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments; often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, knives) due to its sharp edges; used today in construction aggregate, road surfacing, and as a component in ceramics.

Geological facts

Chert exhibits conchoidal fracture, meaning it breaks with smooth, curved surfaces similar to glass. It was one of the most important minerals for early human survival for both tool-making and fire-starting.

Field identification & locations

Identify in the field by its hardness (it can scratch glass), its waxy or dull luster, and its characteristic curved, sharp break patterns. Commonly found in riverbeds or limestone outcrops.