sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, blue-gray, brown, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray, blue-gray, brown, tan
Luster: Waxy to dull

Identified May 21, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray, blue-gray, brown, tan; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids within sedimentary rock layers, often limestone or chalk.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges; used in construction aggregate and as a spark-generator in flintlock firearms.

Geological facts

Chert is one of the most durable sedimentary rocks. When it strikes steel, it creates sparks, which made it essential for early fire-starting and weaponry.

Field identification & locations

Identify in the field by its smooth, waxy surface and its distinct conchoidal (shell-like) fracture patterns that create razor-sharp edges. Commonly found in stream beds or limestone outcrops.