sedimentary

Chert (Jasper/Flint variety)

Microcrystalline quartz (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Tan, brown, and yellowish-orange. Luster: Dull to waxy. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None, exhibits conchoidal (shell-like) fracture. Specific gravity: 2.65.

Hardness: 6
Color: Tan, brown, and yellowish-orange
Luster: Dull to waxy

Identified April 12, 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 the chemical precipitation of silica in groundwater. Can be found in various geological ages, often replacing limestone or dolostone through chemical substitution.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges when broken. Today used in construction aggregate, road surfacing, jewelry (as Jasper varieties), and as a collector's item.

Geological facts

Chert is so hard that it will spark when struck against steel, which is why the 'Flint' variety was critical for early firearms and fire-starting tools. It is also highly resistant to chemical weathering.

Field identification & locations

Identify in the field by its smooth, waxy feel, extreme hardness (it will scratch glass), and the way it breaks into curved, sharp fragments. Common in riverbeds and limestone outcrops.

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