sedimentary

Chert (specifically Red Chert / Jasper)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Reddish-orange, brown, and tan due to iron inclusions; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.7

Hardness: 7 on Mohs scale
Color: Reddish-orange, brown, and tan due to iron inclusions
Luster: Waxy to vitreous

Identified March 25, 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 chemical precipitation from hydrothermal fluids in marine environments. Often found in nodules within limestone or as bedded deposits.

Uses & applications

Historically used for stone tools and weapons due to sharp conchoidal fracturing. Modernly used in jewelry (as a gemstone), road construction material, and as an abrasive.

Geological facts

Because of its hardness and brittleness, it was the primary material for arrowheads and scrapers for thousands of years. It can create sparks when struck against steel, similar to flint.

Field identification & locations

Identify in the field by its waxy appearance and 'clamshell-like' (conchoidal) breaks. It cannot be scratched by a steel knife. Common in the American Southwest and riverbeds globally.

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Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

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