sedimentary

Chert (Jasper/Flint variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Variegated gray, brown, and reddish-orange due to iron oxides; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Luster: Waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by chemical precipitation in sedimentary basins. It often occurs as nodules or beds within limestone or chalk formations.

Uses & applications

Historically used for stone tools and weapons due to sharp conchoidal edges; currently used for road surfacing, lapidary work (cabs), jewelry, and as flint for fire-starting kits.

Geological facts

Chert is so dense and hard that it was the primary material for the Stone Age 'industry.' Its spark-producing capabilities when struck against steel made it essential for flintlock firearms and early survival technology.

Field identification & locations

Identify by its characteristic 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel knife. Commonly found in riverbeds, glacial tills, or embedded in limestone cliffs. Collectors should look for unique banding or bright iron inclusion colors.

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