Chert (Jasper/Flint variety)

Physical Properties

Hardness: 7 on Mohs scale; Color: Yellowish-orange/Tan with iron staining; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed from the accumulation of silica-rich microfossils or via chemical precipitation in sedimentary environments. Its age can range from Precambrian to recent times.

Uses & Applications

Historically used for stone tools and arrowheads; currently used as landscaping stone, abrasive, or for lapidary work (jewelry and cabochons).

Geological Facts

Chert was one of the most vital materials for early humans due to its ability to fracture into sharp edges. The yellow/orange color is typically caused by goethite or limonite impurities.

Field Identification & Locations

Identify by its waxy appearance and shell-like (conchoidal) fracture pattern. It will scratch glass easily. Found globally in limestone and chalk beds or as gravel in riverbeds.

Identified on: 4/14/2026

Mode: Standard