sedimentary

Chert / River Cobble

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: tan, grey, and black banding, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6

Hardness: 6

Identified July 6, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: tan, grey, and black banding, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; subsequently rounded and smoothed by water transport in a river or coastal environment.

Uses & applications

Used historically for stone tools and today for road construction, landscaping, and as decorative river stones.

Geological facts

This specimen shows distinctive black veining or 'pressure solution' lines called stylolites, or possibly carbonaceous inclusions. Chert is a common find in riverbeds because it is harder than most surrounding rocks and survives long-distance transport.

Field identification & locations

Identify by its hardness (cannot be scratched by a steel knife), waxy luster on fresh surfaces, and smooth, water-worn exterior. Commonly found in gravel pits and along riverbanks.