sedimentary

Chert / Flint

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Gray, tan, or white with a weathered dusty exterior; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Gray, tan, or white with a weathered dusty exterior
Luster: Waxy to dull

Identified May 21, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Gray, tan, or white with a weathered dusty exterior; Luster: Waxy to dull; 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 in marine environments. This specimen shows a weathered, rounded exterior typical of glacial or river transport.

Uses & applications

Historically used for stone tools and starting fires (flint). Currently used in road construction, as an abrasive, and for decorative landscaping.

Geological facts

Because it breaks with a conchoidal fracture like glass, it creates extremely sharp edges; it was the primary material for prehistoric arrowheads and knife blades.

Field identification & locations

Look for a smooth, waxy interior when broken and a sharp, glass-like edge. It is commonly found in limestone beds or as loose gravel in riverbeds and glacial tills.