Chert (White Chert / Flint)

Physical Properties

Hardness: 7 on Mohs scale; Color: Pure white to off-white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolarians or sponge spicules) or by the replacement of carbonate minerals in limestone/chalk. Found in sedimentary layers of various ages.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as road surfacing, in ceramics, and as a component in concrete.

Geological Facts

Because it breaks with a conchoidal fracture (smooth, curved surfaces), it was the primary material for prehistoric humans to craft weapons. It is chemically very stable and resistant to weathering.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by steel) and curved, glass-like fracture surfaces. Often found as nodules within limestone or chalk beds.

Identified on: 4/27/2026

Mode: Standard