sedimentary

Chert Pebble

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, yellowish-brown with bandings. Luster: Waxy to dull. Crystal structure: Cryptocrystalline/microcrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.58-2.64.

Hardness: 6
Color: Tan, brown, yellowish-brown with bandings
Luster: Waxy to dull

Identified July 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from groundwater or accumulation of siliceous organism remains (like radiolarians or diatoms) in marine or freshwater sedimentary environments. Smooth, rounded shape results from water erosion in stream or beach environments.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modern uses include river rock landscaping, construction aggregate, and lapidary tumbling.

Geological facts

Chert is one of the most common rocks used by prehistoric humans to start fires when struck against iron or pyrite (flint is a dark variety of chert). Highly resistant to chemical weathering.

Field identification & locations

Look for a smooth, rounded surface with a waxy appearance, hard enough to scratch glass (hardness > 6). Commonly found along stream beds, gravel bars, rivers, and coastal beaches worldwide.