sedimentary

Chert (variously known as Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Brown, gray, or tan with a waxy luster. Crystal structure: Hexagonal (microscopic). Breakage: Conchoidal (shell-like) fracture. High density and very sharp edges when broken.

Color: Brown, gray, or tan with a waxy luster

Identified April 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater within limestone or chalk beds. Most common in Paleozoic and Mesozoic strata.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and as striker stones for flintlock firearms. Currently used in road surfacing and as a component in some ceramics.

Geological facts

Chert was one of the most important minerals for early humans due to its ability to be knapped into extremely sharp tools. It is so hard that it can scratch steel and produce sparks when struck against iron.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it won't be scratched by a knife), and smooth, curved fracture surfaces. Often found as nodules within limestone or as river-worn pebbles.