sedimentary

Chert (Nodule)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish-white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Tan, brown, or grayish-white
Luster: Dull to waxy

Identified March 17, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish-white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like diatoms) in limestone or chalk beds. Most specimens date from the Phanerozoic eon.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp conchoidal fracture. Industrially used as abrasive or in road construction. Small nodules are common for rock collecting and tumbling.

Geological facts

Chert is so hard it can scratch steel and was used by prehistoric humans to create fire by striking it against iron pyrite. It exists in many varieties, including flint and jasper.

Field identification & locations

Identify in the field by its waxy texture and shell-like (conchoidal) fractures. It is commonly found embedded in limestone outcrops or as weathered nodules in riverbeds across the United States and Europe.