sedimentary

Chert (Chert Nodule)

Silicon Dioxide (SiO₂)

Hardness: 7 on Mohs scale; Color: typically white, tan, gray, or brown; Luster: waxy to dull; Crystal structure: microcrystalline/cryptocrystalline (hexagonal system at microscopic level); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

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

Identified March 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from groundwater or the accumulation of siliceous remains (like diatoms or radiolarians) within limestone or chalk beds. Most specimens date from the Phanerozoic eon.

Uses & applications

Used historically for stone tools (flintknapping) due to its sharp edges; industrially used as an abrasive, in road construction, and occasionally tumbled for jewelry or aquarium gravel.

Geological facts

Chert is so hard it can scratch glass and steel. High-quality varieties are known as Flint; when it contains specific patterns or colors, it may be classified as Jasper or Agate.

Field identification & locations

Identify in the field by its waxy texture and conchoidal (shell-like) fractures. It is commonly found in gravel pits, riverbeds, or weathered out of limestone outcrops globally.