Chert (White Flint)

Physical Properties

Hardness: 7 on Mohs scale; Color: White to off-white with tan weathering; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.

Uses & Applications

Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used in construction aggregate, road surfacing, and as a raw material for ceramics.

Geological Facts

Chert is so hard it can scratch steel and was commonly used alongside high-carbon steel to create sparks for starting fires in the form of 'flint and steel'.

Field Identification & Locations

Identify by its waxy texture and shell-like (conchoidal) fractures. Often found as nodules within limestone or as river-worn cobbles. It will not react with acid, unlike limestone.

Identified on: 5/1/2026

Mode: Standard