sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Dark brown to black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Dark brown to black
Luster: Waxy to dull

Identified June 6, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Dark brown to black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily through the chemical precipitation of silica-rich fluids in sedimentary environments. Often found as nodules in limestone or chalk beds, frequently dating back to the Mesozoic or Paleozoic eras.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road surfacing, in ceramics, and as a starting material for fire-striking (flint and steel).

Geological facts

Flint is a variety of chert that occurs specifically in chalk or marly limestone. It was the primary technological resource for humans for over two million years.

Field identification & locations

Identify in the field by its incredibly smooth, shell-like (conchoidal) fracture pattern and its ability to scratch glass. It is commonly found in riverbeds or eroding out of limestone cliffs.