sedimentary

Chert / Flint

Silicon Dioxide (SiO2)

Hardness: 7 on the Mohs scale; Color: Tan, brown, yellowish, grey, with dark speckles; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (shows conchoidal fracture); Specific gravity: ~2.65

Hardness: 7 on the Mohs scale
Color: Tan, brown, yellowish, grey, with dark speckles
Luster: Waxy to dull

Identified July 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms in sedimentary environments through the accumulation of siliceous organism remains (like diatoms or radiolarians) or chemical precipitation of silica in groundwater within limestone and chalk beds.

Uses & applications

Historically used for making stone tools, arrowheads, and spark-striking tools. Today used in road construction aggregate, landscaping, and lapidary collections.

Geological facts

Chert breaks with extremely sharp edges, known as conchoidal fracture, which made it one of the most important raw materials for prehistoric humans during the Stone Age.

Field identification & locations

To identify in the field, look for a smooth, waxy surface with sharp broken edges that easily scratch steel or glass. Commonly found along riverbeds, beaches, and weathered limestone outcrops.