Chert / Jasper

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and cream; Luster: Waxy to vitreous; Structure: Microcrystalline (no visible grains); Cleavage: None (conchoidal fracture).

Formation & Geological History

Formed through the accumulation of silica-rich microfossils or chemical precipitation from silica-rich fluids in sedimentary environments. Can also occur as nodules in limestone or as bedded deposits.

Uses & Applications

Historically used for stone tools (edges are razor sharp). Modern uses include gemstones, landscaping, and lapidary polishing. Because it is chemically stable, it is also used in some industrial abrasives.

Geological Facts

Chert is one of the most durable rocks in the geological record. Ancient humans specifically sought it out for flint knapping because of its predictable conchoidal fracture pattern.

Field Identification & Locations

Identify in the field by its waxy texture and sharp, shell-like (conchoidal) breaks. It cannot be scratched by a steel knife. Frequently found in riverbeds, desert pavements, and limestone outcrops.

Identified on: 4/28/2026

Mode: Standard