sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Tan, grey, creamy white. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.5-2.8.

Hardness: 7 on Mohs scale
Color: Tan, grey, creamy white
Luster: Waxy to dull

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale. Color: Tan, grey, creamy white. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.5-2.8.

Formation & geological history

Formed primarily through the precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like diatoms or radiolarians) in marine environments. It is often found as nodules or layers within limestone and chalk beds.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used as a gemstone (jasper/agate varieties), in road construction aggregate, and as a geological specimen.

Geological facts

Chert has a conchoidal fracture, which allows it to break into pieces with very sharp edges. This made it the primary material for arrowheads and scrapers for prehistoric humans for thousands of years.

Field identification & locations

Identify in the field by its waxy appearance and shell-like (conchoidal) fracture pattern when broken. It cannot be scratched by a steel knife. Common in limestone regions and streambeds.