sedimentary

Chert Nodule

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, and grey with a white weathered cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).

Hardness: 7 on Mohs scale
Color: Brown, tan, and grey with a white weathered cortex
Luster: Waxy to dull

Identified June 4, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, tan, and grey with a white weathered cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).

Formation & geological history

Forms through the chemical precipitation of silica-rich fluids within sedimentary rock layers like limestone or chalk. Often contains microfossils and forms in marine environments over millions of years.

Uses & applications

Historically used for stone tools (flintknapping) due to its sharp edges when broken. Today used as a road aggregate, in landscaping, and as a semi-precious stone when polished.

Geological facts

Flint is a variety of chert. This specimen shows a classic rounded nodule shape with a partially worn white outer coating known as a cortex.

Field identification & locations

Identified by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in riverbeds or eroding out of limestone cliffs.