sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, shows conchoidal fracture; Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: typically tan, brown, or gray
Luster: waxy to dull

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, shows conchoidal fracture; Specific gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation from groundwater within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to sharp edges when fractured. Currently used in road construction, as an abrasive, and sometimes for jewelry (as jasper or agate varieties).

Geological facts

Chert was one of the most important materials for early humans; its ability to produce sharp flakes made it essential for arrowheads, scrapers, and starting fires with steel.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found as nodules in limestone regions.