sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 6.5–7 on Mohs scale. Color: Red, brown, and tan due to iron oxide impurities. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58–2.91.

Hardness: 6
Color: Red, brown, and tan due to iron oxide impurities
Luster: Dull to waxy

Identified March 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or through chemical precipitation in sedimentary basins. The red hues indicate the presence of hematite or other iron oxides during the petrification or replacement process.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges when fractured. Currently used in jewelry (cabochons), as an ornamental stone, and in landscaping.

Geological facts

Chert and its variety, jasper, have been used by humans for over 2 million years to create tools. Its characteristic conchoidal fracture allows it to be 'knapped' into extremely sharp blades.

Field identification & locations

Identify in the field by its wax-like luster on fresh breaks, lack of visible crystals, and ability to scratch glass easily. Commonly found in riverbeds, desert pavements, and as nodules within limestone or chalk layers.

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