sedimentary

Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Brownish-red to tan. Luster: Dull to waxy. Crystal structure: Microcrystalline/cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 6
Color: Brownish-red to tan
Luster: Dull to waxy

Identified June 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine or groundwater environments. Jasper is a common variety of chert containing iron oxide impurities that give it its reddish-brown hue.

Uses & applications

Historically used for stone tools (arrowheads). Modernly used for lapidary work, jewelry, pocket stones, and decorative gravel.

Geological facts

Chert was one of the most important minerals for early humans due to its ability to fracture with extremely sharp edges. It is chemically identical to quartz but has a different internal structure.

Field identification & locations

Identify by its hardness (will scratch glass), smooth waxy feel when wet, and conchoidal (shell-like) fracture patterns. Frequently found as pebbles in riverbeds or as nodules in limestone.