sedimentary

Chert (River Pebble)

Microcrystalline silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray with yellowish-brown iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray with yellowish-brown iron staining
Luster: Waxy to dull

Identified June 4, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray with yellowish-brown iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed from the precipitation of silica from seawater or groundwater, often replacing organic material or carbonate. This specimen is a water-worn river pebble, likely shaped over thousands of years by fluvial erosion.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; currently used as construction aggregate, road base, and occasionally for lapidary tumbling.

Geological facts

Chert was one of the most important minerals for early human survival, used globally for flint-knapping into tools and fire-starting (flint is a high-purity variety of chert).

Field identification & locations

Identify by its hardness (will scratch glass), smooth texture, and waxy luster. Look for it in riverbeds, glacial deposits, or embedded in limestone outcrops.