sedimentary

Chert (Jasper/Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 6.5–7 (Mohs scale); Color: Brownish-gray to olive green; Luster: Waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: None (fractures conchoidally); Specific gravity: 2.6–2.7

Hardness: 6
Color: Brownish-gray to olive green
Luster: Waxy to dull

Identified April 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from hydrothermal fluids. It typically develops in marine environments as nodules within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads and scrapers) due to its sharp edges. Modern uses include decorative gravel, landscaping, and occasionally as a source of silica for industrial purposes.

Geological facts

Because of its conchoidal fracture pattern, chert breaks into incredibly sharp edges—sharper than a steel scalpel. It was one of the most vital raw materials for early humans worldwide.

Field identification & locations

Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fracture surfaces. It cannot be scratched by a steel knife but will scratch glass easily. Found globally in sedimentary basins.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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