sedimentary

Chert (Nodule)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: Varies (commonly grey, tan, brown, or white), Luster: Waxy to dull, Crystal Structure: Cryptocrystalline (microscopic quartz), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 – 2.7

Identified March 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich marine organisms (like radiolaria or sponges) or by the precipitation of silica from groundwater within limestone or chalk beds. Often paleozoic or mesozoic in age.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Modern uses include road surfacing materials, decorative landscaping, and occasionally as a source of high-purity silica for glass or electronics.

Geological facts

Chert and Flint are essentially the same mineral; however, 'Flint' is usually the name reserved for dark-colored chert found in chalk deposits. Because it is harder than steel, it was used historically to strike sparks for fire.

Field identification & locations

Identify byIts conchoidal fracture (curved, glass-like breaks) and that it cannot be scratched by a steel knife. Commonly found in limestone outcrops or as river-worn pebbles. For collectors, look for unique colors or embedded fossils.