sedimentary

Chert (Yellow/Brown Jasper)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 (Mohs scale); Color: Yellowish-brown, tan, with darker iron oxide staining; Luster: Dull to waxy; Structure: Microcrystalline (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7

Hardness: 6
Color: Yellowish-brown, tan, with darker iron oxide staining
Luster: Dull to waxy

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from silica-rich fluids in sedimentary rock voids. Often found in limestone or as water-worn pebbles in riverbeds.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges when fractured. Modern uses include decorative gravel, lapidary work (polishing for jewelry like necklaces or cabochons), and as a gemstone component.

Geological facts

Chert is incredibly durable and resistant to chemical weathering. Early humans prized this specific rock type because it fractures predictably into razor-sharp edges, a property known as conchoidal fracturing.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, waxy surface when broken. It often feels 'heavier' than common limestone. Commonly found in riverbeds, glacial tills, and coastal areas throughout North America and Europe.