sedimentary

Chert (Pebble)

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs); Color: Brown, grey, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (Triagonal system); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs)
Color: Brown, grey, tan
Luster: Waxy to dull

Identified April 1, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Brown, grey, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (Triagonal system); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary layers. This specific specimen is a water-worn river pebble.

Uses & applications

Historically used for stone tools (arrowheads). Today used in road construction, landscaping, and occasionally as an abrasive or for lapidary tumbling.

Geological facts

Chert is so hard it can strike sparks from steel. Flint is a high-quality variety of chert. Because of its conchoidal fracture, it was the primary material for stone-age weaponry.

Field identification & locations

Identify by its 'waxy' texture, extreme hardness (cannot be scratched by a steel knife), and smooth, curved fracture surfaces. Commonly found in riverbeds, glacial till, and within limestone outcrops.