sedimentary

Chert (Flint nodule)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: tan, yellow-white, or buff; Luster: waxy to dull; Structure: microcrystalline (no visible grains); Fracture: conchoidal (shell-like curves); Specific Gravity: 2.65.

Hardness: 6
Color: tan, yellow-white, or buff
Luster: waxy to dull

Identified July 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine sedimentary environments through the precipitation of silica-rich fluids within limestone or chalk beds. This specimen appears to be a weathered nodule, potentially from the Cretaceous or Jurassic periods.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as road surfacing, in some ceramics, and as a starting material for fire-striking flint.

Geological facts

Chert was one of the most important minerals for early humans because of its predictable conchoidal fracture, which allows it to be knapped into sharp tools. It is chemically identical to quartz but with a different internal structure.

Field identification & locations

Identify in the field by its waxy appearance, extreme hardness (it will scratch glass), and curved fracture surfaces. Commonly found in limestone outcrops, river beds, and coastal chalk cliffs.

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