sedimentary

Flint (Chert)

Cryptocrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Gray, tan, and white mottled with a waxy to dull luster; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs
Color: Gray, tan, and white mottled with a waxy to dull luster

Identified March 12, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Gray, tan, and white mottled with a waxy to dull luster; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed as nodules or masses in sedimentary rocks like chalk or limestone through the replacement of calcium carbonate with silica-rich groundwater. Often dates to the Cretaceous or Jurassic periods.

Uses & applications

Historically used for stone tools and strike-a-lights; currently used in construction aggregate, road surfacing, jewelry as flint knapping art, and as a component in ceramics.

Geological facts

Flint was the primary material for prehistoric humanity's weapons. It has the rare property of sparking when struck against steel, which pioneered fire-starting and early firearms like flintlocks.

Field identification & locations

Identified in the field by its distinctive sharp shell-like (conchoidal) fractures and waxy texture. Commonly found in chalk downs or coastal cliffs, specifically in the UK, France, and parts of the US like Ohio.