sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Tan, brown, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Hardness: 6
Color: Tan, brown, or gray
Luster: Waxy to dull

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, brown, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms) or by chemical precipitation in saltwater or freshwater environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and starting fires. Today used as a decorative stone, in construction aggregate, and as a polishing media in lapidary work.

Geological facts

Chert was one of the most vital materials for prehistoric humans because it breaks into very sharp edges via conchoidal fracture. It is often referred to as 'stone age steel'.

Field identification & locations

Identify in the field by its waxy appearance and shell-like (conchoidal) fractures. It will scratch glass and often gives off sparks when struck against steel. Found globally in sedimentary rock formations.