sedimentary

Chert (Pebble)

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Grayish-blue to dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Grayish-blue to dark grey
Luster: Waxy to dull

Identified May 27, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grayish-blue to dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater within sedimentary rock layers, often found in limestone or chalk beds.

Uses & applications

Historically used for stone tools/arrowheads due to its sharp edges when broken; used modernly in road construction, as decorative gravel, and occasionally for high-durability laboratory equipment parts.

Geological facts

Chert is so hard it can strike sparks from steel, which led to its subtype 'flint' being used in early firearms and fire-starting kits. It is exceptionally resistant to weathering.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in riverbeds or coastal areas as weathered pebbles.