sedimentary

Chert (River Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, brown, and grey with iron oxide staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, brown, and grey with iron oxide staining
Luster: Waxy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine or freshwater environments. This specific specimen appears to be a rounded river cobble, suggesting mechanical weathering and transport over a long geological period.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to its sharp edges. Currently used as construction aggregate, road base, and occasionally as decorative landscaping stone.

Geological facts

Chert is so durable that it often survives the weathering of its original host rock. It is one of the most common materials found in riverbeds worldwide. When struck with steel, high-quality chert can produce sparks.

Field identification & locations

Identified in the field by its hardness (cannot be scratched by a steel knife), smooth rounded texture if water-worn, and conchoidal (shell-like) fracture patterns if broken. Common in limestone regions and gravel bars.