sedimentary

Chert (Jasper/Black Chert)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Dark grey to black with brown weathering rind, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified April 19, 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 chemical precipitation from hydrothermal fluids in deep-sea or sedimentary environments. Most specimens range from Precambrian to Cenozoic eras.

Uses & applications

Historically used for stone tools/weapons (arrowheads); currently used in construction aggregate, landscaping, lapidary arts (tumbled stones), and as a silica source in glassmaking.

Geological facts

Chert is a variety of quartz that was the 'high-tech' material of the Stone Age because it fractures consistently into sharp edges. Black chert is often called 'flint' if it occurs in chalk or limestone beds.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in riverbeds, glacial deposits, and as nodules within limestone or dolomite cliffs.