Chert (Flint variety)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: tan, grey, brown; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in sedimentary environments. Can be found in nodules within limestone or chalk beds.

Uses & Applications

Historically used for stone tools and weapons (arrowheads); currently used as an abrasive, in road construction, and for 'flint and steel' fire starting.

Geological Facts

Chert was one of the first materials used by early humans to create tools due to its ability to split into thin, sharp edges through conchoidal fracturing. Known as flint when found in chalk or marly limestone.

Field Identification & Locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and its characteristic shell-like (conchoidal) curved fractures. Common in riverbeds and limestone outcrops.

Identified on: 4/28/2026

Mode: Standard