sedimentary

Chert (River Pebble)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Dark grey/brown with tan banding; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65

Hardness: 7 Mohs scale
Color: Dark grey/brown with tan banding
Luster: Dull to waxy

Identified June 28, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Dark grey/brown with tan banding; Luster: Dull to waxy; Structure: Cryptocrystalline/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65

Formation & geological history

Formed via the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. This specimen has been rounded and smoothed by fluvial (river) erosion over thousands of years.

Uses & applications

Historically used for stone tools and fire-starting. Currently utilized in construction aggregate, landscaping, and as decorative river stones.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has weathered away. It was a primary material for prehistoric arrowheads due to its sharp conchoidal fracturing.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth texture, and characteristic waxy luster when broken. Frequently found in riverbeds, glacial tills, and limestone deposits worldwide.