sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Yellowish-brown to reddish-brown (ochre); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Yellowish-brown to reddish-brown (ochre)
Luster: Waxy to dull

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Yellowish-brown to reddish-brown (ochre); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Formation & geological history

Formed from the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary basins. The brown color is due to iron oxide (limonite/hematite) inclusions.

Uses & applications

Used historically for stone tools due to sharp edges; currently used for lapidary work, tumbled stones, landscaping, and as a source of high-purity silica.

Geological facts

Chert has been used by humans for hundreds of thousands of years to create arrowheads and scrapers. Because of its hardness, it can spark when struck against steel, leading to its historical use in flintlock firearms.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy luster on fresh surfaces, and smooth, curved (conchoidal) fractures. Frequently found as nodules in limestone or as stream-rolled river pebbles.