sedimentary

Chert (Flint)

Microcrystalline quartz (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: typically gray, tan, or brown with waxy luster; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: typically gray, tan, or brown with waxy luster

Identified January 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5–7 on Mohs scale; Color: typically gray, tan, or brown with waxy luster; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed primarily through the chemical precipitation of silica-rich fluids in marine or groundwater environments. It often occurs as nodules or layers within limestone or chalk beds, frequently dating from the Paleozoic, Mesozoic, or Cenozoic eras.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and starting fires (flint and steel). Modern uses include aggregate for construction, road surfacing, and as a raw material for ceramics.

Geological facts

Flint is a variety of chert that occurs specifically in chalk or marl. It has been vital to human survival for millennia due to its sharp edges and its ability to spark when struck against steel or iron pyrites.

Field identification & locations

Identify in the field by its very smooth, waxy surface and its characteristic conchoidal (shell-like) fracture patterns. It is commonly found in gravel pits, riverbeds, or as nodules embedded in cliff faces made of softer sedimentary rock.