sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, beige, brown
Luster: Waxy to dull

Identified July 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as nodules or beds in sedimentary rocks (like limestone) through the accumulation of silica-rich organic remains or chemical precipitation. Primarily found in Phanerozoic strata.

Uses & applications

Historically used for stone tools and starting fires (striking steel). Modernly used in road construction, and higher quality varieties are used for jewelry and lapidary art.

Geological facts

Chert has a conchoidal fracture, similar to glass, which allows it to be broken into extremely sharp edges. It was the primary material for arrowheads and scrapers for thousands of years.

Field identification & locations

Identify in the field by its waxy texture and shell-like (conchoidal) fracture pattern when broken. It will easily scratch glass and cannot be scratched by a steel knife.