sedimentary

Rounded chert or silicified limestone pebble

Microcrystalline quartz (SiO₂), possibly fossiliferous or iron-stained carbonate host

AI-generated identification · may be incorrect

Hardness about 6.5–7 for chert, brown to gray with earthy/waxy luster, cryptocrystalline texture, and no visible cleavage; the pale spots may be weathered carbonate or fossil fragments. Exact identification is limited by the photograph.

Identified September 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely a water-worn sedimentary pebble formed by silica replacement or cementation in marine or continental sediments, then rounded by stream or beach transport. The formation age cannot be determined visually.

Uses & applications

Common chert is used locally as aggregate, road material, and historically for sharp tools; attractive polished pieces are collected, but this specimen has little commercial value.

Geological facts

Chert commonly produces a sharp conchoidal fracture and may preserve radiolarians, shells, or other fossils. Brown coloration often results from iron oxides.

Field identification & locations

Look for a glassy wax-like surface, very high hardness, and inability to scratch it with a steel knife; vinegar fizz would suggest exposed limestone instead. Chert occurs worldwide, especially in limestone and other sedimentary formations.