sedimentary

Chert (Jasper/Flint Pebble)

Microcrystalline quartz (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Tan, brown, and yellowish-orange due to iron oxide staining; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Tan, brown, and yellowish-orange due to iron oxide staining
Luster: Waxy to dull

Identified May 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the precipitation of silica-rich fluids within sedimentary rock layers, often replacing organic matter or limestone. This specimen appears to be a stream-rounded or weathered pebble from the Quaternary or Tertiary period.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges when broken. Today used in gravel for construction, as landscaping stones, and occasionally for lapidary work.

Geological facts

Chert was one of the most important minerals for early humans because of its ability to fracture conchoidally, producing edges sharper than a steel scalpel. Varieties like flint and jasper are different color forms of the same mineral.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Found globally in riverbeds, glacial tills, and sedimentary outcrops.

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