sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs. Color: Tan, beige, gray, or white. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 6
Color: Tan, beige, gray, or white
Luster: Waxy to dull

Identified July 8, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs. Color: Tan, beige, gray, or white. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the displacement of calcium carbonate in limestone by silica-rich fluids. Often found in nodules or bedded layers.

Uses & applications

Historically used for stone tools and starting fires. Modernly used as road aggregate, architectural stone, and occasionally for lapidary work.

Geological facts

This specimen shows classic conchoidal (shell-like) fracturing, which is why it was favored by prehistoric humans for knapping into arrowheads and knives. It is highly resistant to weathering.

Field identification & locations

Look for a smooth, waxy texture and sharp, curved edges where broken. It will scratch glass. It is commonly found in limestone or chalk deposits, or as river pebbles.