sedimentary

Chert / Pink Chert

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Pink, tan, white, and brown; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.65.

Hardness: 7 (Mohs scale)
Color: Pink, tan, white, and brown
Luster: Waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation of silica-rich fluids. Often found as nodules or bedded deposits in limestone or dolostone across various geological ages from Precambrian to Cenozoic.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in geological research, as decorative landscaping stone, and occasionally in jewelry as cabochons.

Geological facts

Chert is essentially the same material as flint, though the term 'flint' is often reserved for dark gray or black varieties found in chalk. It is highly resistant to weathering and is often found as loose stones in stream beds well after the surrounding rock has eroded.

Field identification & locations

Identify by its waxy appearance and 'conchoidal' fracture (curved, shell-like breaks). It cannot be scratched by a steel knife. Common in the Midwest USA and Appalachian regions. Collectors look for unique banding or 'scenic' inclusions.