sedimentary

Chert (Varietal Agate/Jasper)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brown, tan, reddish-orange with white matrix; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65

Hardness: 6
Color: Brown, tan, reddish-orange with white matrix
Luster: Waxy to vitreous

Identified June 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater in cavities of other rocks or through the accumulation of siliceous oozes in marine environments. Often found in limestone or volcanic host rocks.

Uses & applications

Used historically for stone tools due to conchoidal fracture; modernly used in jewelry (cabbing), lapidary art, and as decorative landscape stone.

Geological facts

Chert was one of the first materials used by early humans to create arrowheads and scrapers. The reddish varieties are often called Jasper, while translucent banded varieties are Agate.

Field identification & locations

Identify by its hardness (will scratch glass), waxy luster on broken surfaces, and lack of visible crystals. Commonly found in river beds or eroded out of limestone cliffs.