Chert (Jasper variation)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and cream; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the accumulation of silica-rich biogenic material or by the replacement of carbonate minerals with silica in sedimentary environments. Common in marine and lacustrine deposits.

Uses & Applications

Historically used for stone tools (knapping); modernly used for lapidary work, jewelry (beads and cabochons), and as a decorative stone.

Geological Facts

Chert has a conchoidal fracture which allows it to break into sharp edges, making it the primary material for prehistoric arrowheads and scrapers. Jasper is a variety of chert colored by iron oxides.

Field Identification & Locations

Identify in the field by its hardness (it can scratch glass), waxy luster, and shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or as nodules in limestone.

Identified on: 5/1/2026

Mode: Standard