sedimentary

Chert (River Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Tan, beige, gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Tan, beige, gray
Luster: Waxy to dull

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Tan, beige, gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. This specimen shows significant rounding from fluvial (river) or beach wear.

Uses & applications

Historically used for stone tools (flint knapping); currently used as drainage gravel, road base, and occasionally as decorative landscaping stone.

Geological facts

Chert can contain microfossils. It is extremely chemically stable and hard, which allows it to survive long-distance transport in rivers, becoming the smooth pebbles often found on beaches and in stream beds.

Field identification & locations

Identify by its smooth, waxy feel, conchoidal (shell-like) fracture patterns where broken, and high hardness (it will scratch glass). Found globally in sedimentary basins.