sedimentary

Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Brown, tan, and dark grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Brown, tan, and dark grey
Luster: Waxy to dull

Identified May 31, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Brown, tan, and dark grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine or lacustrine environments; specimens like this are often rounded by fluvial (water) erosion.

Uses & applications

Historically used for stone tools due to sharp edges; currently used for landscaping, jewelry (when polished), and as an indicator of sedimentary basins.

Geological facts

Chert is a cryptocrystalline variety of quartz. Brown-toned opaque chert is often colloquially referred to as Jasper. It was one of the most important materials for early humans to create knapped projectile points.

Field identification & locations

Identify in the field by its smooth, waxy texture and curved, glass-like (conchoidal) fractures. Found worldwide in riverbeds, beaches, and sedimentary rock outcrops.