sedimentary

Chert (and Jasper/Chalcedony mixture)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: brown, tan, creamy white, and gray. Luster: waxy to vitreous. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 6
Color: brown, tan, creamy white, and gray
Luster: waxy to vitreous

Identified May 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation in hydrothermal or sedimentary environments in marine or volcanic settings.

Uses & applications

Used historically for stone tools (arrowheads). Modern uses include gemstones, landscaping, and industrial abrasives.

Geological facts

Chert is so hard it can produce sparks when struck against steel, which made it a critical survival material for early humans. Its colors are usually due to trace amounts of iron or manganese oxides.

Field identification & locations

Look for a glassy/waxy surface and sharp, curved (conchoidal) edges where the stone has chipped. It will scratch glass and cannot be scratched by a steel knife. Frequently found in riverbeds or within limestone layers.