Chert (Jasper)

Physical Properties

Hardness: 6.5-7 Mohs; Color: Brownish-yellow, tan, or ochre; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments; common in Paleozoic to Cenozoic strata.

Uses & Applications

Used historically for stone tools and arrowheads; today used for decorative gravel, jewelry (cabochons), and as a landscape stone.

Geological Facts

This variety of chert is often called Jasper when it is opaque and colored by iron oxides. It breaks with a sharp edge, making it a primary material for prehistoric lithic technology.

Field Identification & Locations

Identify by its waxy luster on fresh surfaces, extreme hardness (scratches glass), and characteristic curved conchoidal fractures. Commonly found in stream beds or limestone outcrops.

Identified on: 5/18/2026

Mode: Standard