sedimentary

Chert / Jasper

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs), Color: Brown, red, orange, yellow, Luster: Waxy to dull, Crystal structure: Microcrystalline quartz, Cleavage: None (conchoidal fracture)

Hardness: 6

Identified June 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs), Color: Brown, red, orange, yellow, Luster: Waxy to dull, Crystal structure: Microcrystalline quartz, Cleavage: None (conchoidal fracture)

Formation & geological history

Formed from the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by chemical precipitation in saltwater or freshwater environments. Often found as nodules within limestone or chalk.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges when fractured. Currently used in jewelry (lapidary), as aquarium gravel, and in road construction.

Geological facts

Chert was one of the most important materials for early humans because its conchoidal fracture allows it to be knapped into extremely sharp arrowheads and knives. Jasper is the name specifically used for colorful, opaque varieties.

Field identification & locations

Look for a smooth, waxy texture and shell-like (conchoidal) fracture patterns. It will scratch glass but cannot be scratched by a steel nail. Commonly found in riverbeds and sedimentary outcrops.