sedimentary

Chert (Chert Nodule)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 7 on Mohs scale (scratches glass); Color: Gray, black, and tan in this specimen; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale (scratches glass)
Color: Gray, black, and tan in this specimen
Luster: Waxy to dull

Identified March 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical replacement of limestone/chalk by silica-rich fluids. It can be found in sedimentary strata dating from the Precambrian to the present.

Uses & applications

Historically used for stone tools and arrowheads. Currently used in road construction, as jewelry (when patterned like jasper/agate), and as flint for spark ignition.

Geological facts

Chert is so hard it was the primary material for the 'Stone Age' because it breaks into sharp, glass-like edges. Dark varieties are often colloquially called 'flint.'

Field identification & locations

Identify by its conchoidal (shell-like) fracture pattern and its ability to scratch glass. Commonly found in stream beds or weathering out of limestone cliffs. Collect by looking for nodules with a white 'rind' or cortex.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

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