sedimentary

Chert (Smooth River Pebble)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Brown, grey, or tan (due to iron impurities); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8.

Hardness: 6
Color: Brown, grey, or tan (due to iron impurities)
Luster: Waxy to dull

Identified March 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments; geological age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as river rock for landscaping.

Geological facts

Chert is so hard it can scratch glass. When struck against steel, it produces sparks, which led to its historical use in flintlock firearms and primitive fire-starting kits.

Field identification & locations

Identify by its 'waxy' appearance and smooth, rounded edges if found in water; it often displays a curved (conchoidal) fracture when broken. Found globally in riverbeds and sedimentary basins.