sedimentary

Chert (Jasper variety)

Silicon dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Brown to reddish-orange (due to iron inclusions); Luster: Dull to waxy; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Brown to reddish-orange (due to iron inclusions)
Luster: Dull to waxy

Identified June 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation in sedimentary environments. Common in marine settings and as nodules in limestone. This sample shows signs of alluvial weathering.

Uses & applications

Historically used for tools and flintknapping. In modern times, used for lapidary jewelry, garden landscaping, and as a semi-precious gemstone when polished.

Geological facts

Chert is so durable that it was once the primary material for prehistoric arrowheads and spear tips because it breaks into sharp, glass-like edges. The brown variety is often influenced by limonite or goethite.

Field identification & locations

Identify by its hardness (it will scratch glass) and its curved, shell-like (conchoidal) fracture pattern. It feels smoother than sandstone and is found in riverbeds and coastal regions worldwide.