sedimentary

Chert (Pebble)

Microcrystalline to Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Non-crystalline mass (amorphous appearance); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified May 27, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Non-crystalline mass (amorphous appearance); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary beds. These specimens are often found as weathered pebbles in secondary deposits.

Uses & applications

Primarily used historically for stone tools and weapons due to its sharp edges; currently used for road ballast, landscaping, and as a raw material for silicon production.

Geological facts

Chert is a very hard and durable rock that can spark when struck against steel. Flint is a high-quality variety of chert often associated with chalk or limestone.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy luster when freshly broken, and smooth, curved conchoidal fractures. Common in riverbeds and glacial tills worldwide.