sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, or brown with white weathering; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, beige, or brown with white weathering
Luster: Dull to waxy

Identified May 17, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or brown with white weathering; Luster: Dull to waxy; Structure: 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 from groundwater within limestone or chalk beds. Commonly found in Paleozoic or Mesozoic strata.

Uses & applications

Historically used for stone tools (arrowheads/knives) due to sharp edges when fractured. Modern uses include road surfacing, construction aggregate, and sparked ignition in fire-starting tools.

Geological facts

Chert and flint were some of the first materials used by early humans to create advanced tools. The name 'flint' is often reserved for chert found in chalk or marly limestone.

Field identification & locations

Identified in the field by its extreme hardness (cannot be scratched by steel) and curved, seashell-like (conchoidal) fractures. Common in riverbeds and limestone outcrops. High-quality pieces are sought by 'knappers' (stone tool makers).