sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: tan, brown, or grayish; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like)

Hardness: 7 (Mohs scale), Color: tan, brown, or grayish
Color: tan, brown, or grayish
Luster: waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, brown, or grayish; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like)

Formation & geological history

Formed by the accumulation of silica-rich microfossils or via chemical precipitation in marine or groundwater environments. Found as nodules in limestone or as distinct bedded deposits.

Uses & applications

Historically used for making sharp tools like arrowheads and scrapers. Today used for construction aggregate, road base, and decorative landscaping.

Geological facts

Chert is so hard it can strike sparks from steel. Flint is a well-known dark variety of chert. It is extremely chemically stable and resistant to weathering.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy luster, and conchoidal fracture which creates sharp, curved edges. Frequently found in gravel pits or areas with limestone bedrock.