sedimentary

Chert (Jasper variety)

Cryptocrystalline quartz (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Tan, brown, and reddish-orange due to iron oxide impurities. Luster: Dull to waxy. Structure: Microcrystalline with no visible grains. Cleavage: None (conchoidal fracture). Specific Gravity: 2.5–2.8.

Hardness: 6
Color: Tan, brown, and reddish-orange due to iron oxide impurities
Luster: Dull to waxy

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica-rich fluids within sedimentary rock layers, often replacing limestone or forming as nodules. It can range from Precambrian to recent geological ages depending on the deposit.

Uses & applications

Historically used for stone tools and weapons due to sharp conchoidal edges; currently used in landscaping, as an abrasive, and high-quality colorful pieces are used as decorative gemstones (Jasper) in jewelry.

Geological facts

Because of its extreme hardness and resistance to weathering, chert is often found as 'persistent' pebbles in stream beds long after the surrounding rock has eroded away. Historically, it was essential for starting fires (flint).

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. Commonly found in limestone outcrops or as river-worn cobbles. Collectors look for unique banding or 'brecciated' patterns.

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