Chert (White Chert/Flint)

Physical Properties

Hardness: 7 (Mohs); Color: White, cream, tan with darker inclusions; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline) Quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed through the burial and compaction of silica-rich organic remains (like radiolarians or diatoms) or by the replacement of limestone/dolostone by silica-rich fluids. Can be found in geological strata ranging from Precambrian to Quaternary.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modern uses include road surfacing, concrete aggregate, and as a component in ceramics.

Geological Facts

Chert is so hard it can strike sparks from steel, leading to its historical use in flintlock firearms. The white color is often due to microscopic inclusions of air or water within the quartz matrix.

Field Identification & Locations

Identify in the field by its hardness (will scratch glass), waxy feel, and smooth, curved (conchoidal) breakage patterns. Often found as nodules within limestone or as stream-tumbled cobbles.

Identified on: 4/22/2026

Mode: Standard