sedimentary

Chert (Flint) with Limonite Staining

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Cream, tan, and brown with reddish-orange iron oxide staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 Mohs scale
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine or freshwater environments as a chemical precipitate or through the replacement of limestone by silica-rich fluids. This specimen shows significant weathering and secondary iron oxide (limonite) mineralization on the surface.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; currently used for road ballast, landscaping, and as a collector specimen. Rough flint is also used in ignition systems.

Geological facts

Chert is so durable that it often survives as a 'lag deposit' after the surrounding softer rocks have weathered away. It was one of the most important minerals for early human technological development.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds, limestone outcrops, and coastal areas.

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