sedimentary

Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs). Color: Dark teal-green with brownish-yellow banding. Luster: Waxy to dull. Crystal structure: Microcrystalline/Cryptocrystalline. Cleavage: None, exhibits conchoidal fracture.

Hardness: 6
Color: Dark teal-green with brownish-yellow banding
Luster: Waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich microfossils (like radiolarians) or chemical precipitation from sea water in deep marine environments. This specimen appears water-worn, likely from a river or beach deposit.

Uses & applications

Historically used for making stone tools (arrowheads). Modern uses include lapidary work, jewelry (beads/cabochons), and as a decorative landscaping stone.

Geological facts

Chert was one of the first materials used by early humans due to its ability to break into sharp edges. The variety shown, Jasper, gets its opacity and green hues from iron and silicate inclusions.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), smooth waxy texture, and the shell-like (conchoidal) curves where it has broken. Common in sedimentary basins and as durable river pebbles.