sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically tan, gray, or brown with a white weathered rind (cortex); Luster: waxy to dull; Structure: microcrystalline; Cleavage: none, exhibits conchoidal fracture.

Hardness: 7 on Mohs scale
Luster: waxy to dull

Identified June 27, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically tan, gray, or brown with a white weathered rind (cortex); Luster: waxy to dull; Structure: microcrystalline; Cleavage: none, exhibits conchoidal fracture.

Formation & geological history

Formed through the accumulation of silica-rich biogenic ooze (such as diatoms or radiolarians) or the replacement of limestone/chalk by silica-rich fluids. Often found in Paleozoic or Mesozoic sedimentary basins.

Uses & applications

Historically used for stone tools and flintknapping. Modernly used as road base, decorative landscaping stone, and occasionally in jewelry as jasper.

Geological facts

Chert was one of the most important minerals for prehistoric humans due to its ability to break into razor-sharp edges. It is chemically identical to quartz but has a different microscopic crystal structure.

Field identification & locations

Identify in the field by its very hard surface (can scratch steel), waxy texture, and the presence of a chalky white outer rind. Common in limestone outcrops and riverbeds.