sedimentary

Chert (Jasper)

Silicon dioxide (SiO2)

Hardness: 6.5-7 (Mohs), Color: brownish-tan and grey, Luster: dull to waxy, Crystal structure: microcrystalline (hexagonal/trigonal), Cleavage: none (conchoidal fracture), Specific Gravity: 2.58-2.91

Hardness: 6

Identified June 19, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs), Color: brownish-tan and grey, Luster: dull to waxy, Crystal structure: microcrystalline (hexagonal/trigonal), Cleavage: none (conchoidal fracture), Specific Gravity: 2.58-2.91

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in deep-sea or sedimentary environments. It can also form as nodules in limestone or chalk beds through replacement processes.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges. Currently used in jewelry (as Jasper), lapidary work, and as a decorative stone in landscaping.

Geological facts

Chert and its variety Jasper were some of the most important minerals for early humans because they break with a predictable conchoidal fracture that produces razor-sharp edges.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy luster on fresh surfaces, and smooth, curved (conchoidal) fracture surfaces. Commonly found in river beds or eroded sedimentary outcrops.