sedimentary

Chert (Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Reddish-pink, tan, or brown due to iron inclusions; Luster: Dull to waxy; Crystal Structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.8

Hardness: 6
Color: Reddish-pink, tan, or brown due to iron inclusions
Luster: Dull to waxy

Identified February 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in marine limestone formations.

Uses & applications

Historically used for stone tools/arrowheads due to its sharp fracture edges. Today used in construction aggregate, landscaping, lapidary work (polishing), and as a gemstone for jewelry (beads/cabochons).

Geological facts

Chert and its varieties like Jasper have been used since the Stone Age. When struck against steel, it can produce sparks, making it a primitive tool for fire-starting.

Field identification & locations

Identify in the field by its characteristic smooth, curved (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found in river beds, gravel pits, and eroding out of sedimentary outcrops.

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