sedimentary

Chert (and Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: tan, grey, brown, white; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8.

Hardness: 7 (Mohs scale), Color: tan, grey, brown, white
Color: tan, grey, brown, white
Luster: waxy to dull

Identified July 7, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, grey, brown, white; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8.

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; commonly found in limestone or chalk beds. Most specimens found in decorative mulch like this are from the Cenozoic or Mesozoic eras.

Uses & applications

Historical use for stone tools and weapons (flint knapping); currently used as architectural aggregate, road surfacing, and decorative landscaping stone.

Geological facts

Because it breaks with a conchoidal (shell-like) fracture pattern creating razor-sharp edges, it was the primary material used by prehistoric humans for arrowheads and scrapers.

Field identification & locations

Identify in the field by its waxy texture and sharp, curved fracture points. It will scratch glass easily. Commonly found as nodules or layers within carbonate rock formations.