sedimentary

Chert (Quartz Pebble)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Cream, tan, or light brown with potential darkening; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Cream, tan, or light brown with potential darkening
Luster: Waxy to dull

Identified March 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in sedimentary environments. Common in marine or lake bed deposits; this specific specimen shows rounding from water erosion (fluvial or marine tumble).

Uses & applications

Historically used for stone tools (arrowheads) due to its sharp edges when broken. Modernly used as road aggregate, decorative landscaping stone, and in glass making/industrial abrasives.

Geological facts

Chert is so durable it often survives long after the surrounding rock has eroded away. Prehistoric humans often sought out this specific material for flint-knapping because its microcrystalline structure allows for predictable, razor-sharp fracturing.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, rounded 'river stone' texture. It is ubiquitous in riverbeds and gravel pits worldwide. Collectors should look for unique banding or fossil inclusions.