sedimentary

Chert (Smooth River Pebble)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, brown with mottled patterns; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, brown with mottled patterns
Luster: Dull to waxy

Identified May 3, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, brown with mottled patterns; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater. This specimen has been rounded and smoothed by fluvial (river) action over thousands of years.

Uses & applications

Historically used for stone tools (arrowheads); currently used as decorative landscaping stone, in construction aggregate, and occasionally for lapidary tumbling.

Geological facts

Chert is so hard it can strike sparks against steel. It is one of the most common materials used by prehistoric humans for tool-making because of its predictable conchoidal fracturing.

Field identification & locations

Identify in the field by its waxy texture, inability to be scratched by a steel knife, and smooth, rounded water-worn exterior. Found worldwide in riverbeds, glacial tills, and sedimentary basins.