sedimentary

Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Reddish-brown due to iron oxide impurities. Luster: Dull to waxy. Crystal Structure: Microcrystalline/Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.7.

Hardness: 6
Color: Reddish-brown due to iron oxide impurities
Luster: Dull to waxy

Identified April 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) on the ocean floor, which later undergoes diagenesis, or through the chemical precipitation of silica-rich fluids. This specimen appears water-worn and tumbled.

Uses & applications

Historically used for stone tools (arrowheads/knives) due to its sharp conchoidal fracture. Modernly used in jewelry (as Jasper), lapidary arts, and as landscaping stone.

Geological facts

Jasper is a variety of chert that is opaque and usually colored red or yellow by iron inclusions. It has been used as a gemstone since antiquity and is mentioned in many ancient texts.

Field identification & locations

Identify in the field by its hardness (it can scratch glass), its smooth, waxy feel when wet, and its characteristic conchoidal fracture (shell-like curves). Common in riverbeds and glacial tills.