sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

Hardness: 6.5-7 Mohs; Color: Tan, brown, white with iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 6
Color: Tan, brown, white with iron staining
Luster: Waxy to dull

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, brown, white with iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed primarily from the accumulation of silica-rich organic remains such as radiolaria or diatoms in marine environments, or via chemical precipitation within limestone/chalk beds during the Phanerozoic eon.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to sharp edges; currently used for road ballast, industrial abrasives, and as a decorative stone in collecting.

Geological facts

Chert has been crucial to human evolution; it was one of the first materials used to create specialized tools and to spark fires. It is so tough it can often scratch steel.

Field identification & locations

Identify by its waxy luster, extreme hardness, and distinctive shell-like (conchoidal) fracture pattern. Commonly found in riverbeds or weathered out of limestone formations.