sedimentary

Chert (Jasper)

Cryptocrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Reddish-brown, tan, and gray; Luster: Dull to waxy; Texture: Fine-grained, microcrystalline; Breakage: Conchoidal fracture with sharp edges; Opacity: Opaque.

Hardness: 7 Mohs scale
Color: Reddish-brown, tan, and gray
Luster: Dull to waxy

Identified July 14, 2026More sedimentary →

Explore Chert (Jasper) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7 Mohs scale; Color: Reddish-brown, tan, and gray; Luster: Dull to waxy; Texture: Fine-grained, microcrystalline; Breakage: Conchoidal fracture with sharp edges; Opacity: Opaque.

Formation & geological history

Formed primarily through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from brine in sedimentary basins. This specimen likely contains iron oxide inclusions giving it the reddish jasper-like hue.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modern uses include decorative gravel, lapidary work (tumbled stones), and as a silica source in glassmaking.

Geological facts

Chert is so durable that it often survives as rounded pebbles in riverbeds long after surrounding limestone has eroded away. High-quality red chert is often referred specifically as Jasper in jewelry circles.

Field identification & locations

Identified in the field by its superior hardness (cannot be scratched by a steel knife) and its glass-like, curved fracture surfaces. Commonly found in limestone and dolomite formations or as loose nodules in stream beds.