sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs Scale); Color: Yellowish-brown (limonite staining); Luster: Dull to waxy; Texture: Fine-grained, crypto-crystalline; Conchoidal fracture.

Hardness: 6
Color: Yellowish-brown (limonite staining)
Luster: Dull to waxy

Identified July 3, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs Scale); Color: Yellowish-brown (limonite staining); Luster: Dull to waxy; Texture: Fine-grained, crypto-crystalline; Conchoidal fracture.

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine or groundwater environments. Often associated with limestone and dolostone formations.

Uses & applications

Historically used for stone tools (flintknapping) due to its sharp edges; currently used for lapidary work, tumbled stones, and as decorative gravel.

Geological facts

Chert and its colorful variety Jasper have been used by humans for hundreds of thousands of years to create arrowheads and scrapers. The yellow-brown color is typically due to iron oxide impurities.

Field identification & locations

Identified by its hardness (scratches glass), waxy luster when broken, and lack of visible grains. Found globally in sedimentary basins and as river-worn cobbles.