sedimentary

Chert (Smooth River Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: light gray with darker mottling, Luster: dull/waxy, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.65

Hardness: 6

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: light gray with darker mottling, Luster: dull/waxy, Crystal structure: cryptocrystalline, 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 in marine environments. This specimen has been smoothed by fluvial (river) erosion over thousands of years.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to sharp edges when broken. Industrially used in concrete aggregate and road surfacing. Smaller tumbled pieces are used for landscaping.

Geological facts

Chert is one of the most durable rocks on the planet. Its name comes from the Greek word for 'flint,' and it was essential to early human survival for both tool-making and fire-starting.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and smooth, rounded surface when found in waterbeds. Most common in sedimentary basins globally. Often found as nodules within limestone or dolostone.