sedimentary

Chert (Flint Nodules)

Chert (Cryptocrystalline variety of Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Tan, beige, grey, or white with iron staining (orange/brown); Luster: Dull to waxy; Structure: Cryptocrystalline/microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan, beige, grey, or white with iron staining (orange/brown)
Luster: Dull to waxy

Identified May 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous microfossils (like radiolaria or diatoms) or by chemical precipitation of silica in limestone or chalk beds. Often Cretaceous in age.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges when fractured. Today used in construction aggregate, road base, and as decorative gravel.

Geological facts

Chert is so hard it can scratch steel and glass. It was one of the first materials used by early humans to create fire because striking it against steel produces hot sparks.

Field identification & locations

Identify in the field by its waxy texture, extreme hardness, and 'shell-like' conchoidal fractures. Commonly found in stream beds or weathering out of limestone/chalk cliffs.