sedimentary

Chert / Jasper

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Reddish-brown, tan, and yellow due to iron oxide impurities; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.

Hardness: 6
Color: Reddish-brown, tan, and yellow due to iron oxide impurities
Luster: Waxy to dull

Identified April 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in marine environments. It can also form during diagenesis where silica replaces existing carbonate material.

Uses & applications

Historically used for stone tools and arrowheads because of its sharp conchoidal fracture. Today it is used as a decorative stone, in lapidary work for jewelry, and as aggregate in construction.

Geological facts

Chert is one of the most durable sedimentary rocks. Red chert is frequently called Jasper, and because of its hardness, it remains well-preserved in riverbeds long after softer rocks have eroded away.

Field identification & locations

Identify in the field by its smooth, shell-like fracture (conchoidal), its ability to scratch steel and glass, and its smooth, waxy texture. Commonly found in limestone or dolomite beds as nodules or layers.