sedimentary

Chert (often called Flint)

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs); Color: Tan, brown, gray, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs)
Color: Tan, brown, gray, or white
Luster: Waxy to dull

Identified June 5, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs); Color: Tan, brown, gray, or white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Forms as nodules or layers in limestone or chalk through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from groundwater. It can be found in strata from Precambrian to modern ages.

Uses & applications

Used historically for stone tools (arrowheads, knives) due to its sharp conchoidal fracture. Modernly used as road aggregate, architectural stone, and occasionally for flint-and-steel fire starting.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which made it essential for early flintlock firearms and survival kits. This specimen appears to have edges consistent with knapping or natural fracturing.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a knife), waxy appearance, and smooth, curved (conchoidal) breaks. Often found in creek beds or eroding out of limestone cliffs.