sedimentary

Chert Pebble

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale; Color: Tan to light brown; Luster: Waxy to dull (weathered); Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on the Mohs scale
Color: Tan to light brown
Luster: Waxy to dull (weathered)

Identified March 21, 2026More sedimentary →

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Physical properties

Hardness: 7 on the Mohs scale; Color: Tan to light brown; Luster: Waxy to dull (weathered); Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. This specimen is water-worn and likely found in a riverbed or alluvial deposit.

Uses & applications

Historically used for stone tools and starting fires (flint); currently used as a road aggregate, in landscaping, and as a durable abrasive in grit-blasting.

Geological facts

Chert is so hard that it can scratch steel and glass. Because it breaks with a conchoidal (shell-like) fracture, it was the primary material used by prehistoric humans to create sharp arrowheads and knives.

Field identification & locations

Identify in the field by its extreme hardness and smooth, waxy texture when wet. It will not react with acid, unlike the limestone it is often found in. Commonly found in gravel pits, stream beds, and ocean beaches worldwide.