sedimentary

Chert (River Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and grey with iron staining; Luster: Waxy to dull (glassy when wet); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoïdal fracture); Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Brown, tan, and grey with iron staining
Luster: Waxy to dull (glassy when wet)

Identified June 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through the accumulation of silica-rich microfossils or precipitation from silica-rich fluids. This specimen was secondary-weathered and rounded in a river or fluvial environment.

Uses & applications

Historically used for making stone tools (flintknapping); currently used as architectural aggregate, road surfacing, and as river rock for landscaping.

Geological facts

Chert has been used by humans for millions of years due to its ability to break with very sharp edges. It is chemically identical to quartz but has a different microscopic structure.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel knife), waxy appearance, and smooth, rounded surface if found in water. It is ubiquitous in riverbeds worldwide.