sedimentary

Polished Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 Mohs scale; Color: Dark grey, black, and brownish tones; Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 Mohs scale
Color: Dark grey, black, and brownish tones
Luster: Vitreous to waxy

Identified April 10, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Dark grey, black, and brownish tones; Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or by chemical precipitation. This occurs in marine or groundwater environments over millions of years, often as nodules in limestone or chalk beds.

Uses & applications

Used historically for tool-making (stone age tools), and modernly as a semi-precious stone for jewelry, decorative tumbled stones, and as an industrial abrasive or in the production of ceramics.

Geological facts

Chert is so hard it can strike sparks from steel, which led to its historically vital use in flintlock firearms. It was one of the first materials traded over long distances by prehistoric humans due to its durability and sharpness.

Field identification & locations

Identify in the field by its smooth, waxy surface and distinct shell-like (conchoidal) fractures. Often found in nodes within limestone outcrops or as rounded pebbles in riverbeds and on beaches. Look for its ability to scratch glass.