Chert (Jasper/Flint variety)

Physical Properties

Hardness: 7 (Mohs scale); Color: tan, brown, yellow-brown; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none, exhibits conchoidal fracture.

Formation & Geological History

Formed through the accumulation of silica-rich microfossils or via chemical precipitation in sedimentary basins as modules or lenses. Age varies widely from Precambrian to Cenozoic era.

Uses & Applications

Historically used for making stone tools (arrowheads). Modernly used in lapidary work, jewelry (tumbled stones), and as road ballast or construction aggregate.

Geological Facts

Chert is so hard it can strike sparks from steel, which led to its use in flintlock firearms. It was one of the most vital materials for early human survival for making sharp blades.

Field Identification & Locations

Identify in the field by its waxy luster, smoothness, and distinct shell-like (conchoidal) curves where it is broken; it is harder than a steel knife blade. Common in limestone regions.

Identified on: 4/15/2026

Mode: Standard