sedimentary

Chert Nodule (Flint)

Chert (Silicon Dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, or gray with a lighter weathered cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Tan, brown, or gray with a lighter weathered cortex
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the replacement of limestone or chalk by silica-rich fluids, often accumulating around organic nuclei. These typically date from the Cretaceous to Jurassic periods in marine environments.

Uses & applications

Historically used for stone tools and starting fires; currently used as an abrasive, in road construction, and as a collector's specimen.

Geological facts

Chert is so hard it can scratch steel. When broken, it produces sharp edges which made it the primary material for arrowheads and spear points for thousands of years.

Field identification & locations

Identify in the field by its distinctive 'rind' or cortex and its smooth, shell-like (conchoidal) fracture surface. Frequently found in limestone outcrops or as rounded pebbles in riverbeds.