sedimentary

Chert (Flint Nodular)

Chert (Silicon dioxide, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brown, gray, and cream with a waxy/dull luster; Crystal structure: Microcrystalline/cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, brown, gray, and cream with a waxy/dull luster

Identified March 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation within limestone or chalk beds. Often found as nodules within marine sedimentary layers ranging from the Precambrian to recent eras.

Uses & applications

Historically used for stone tools (knapping) and fire-starting (flint). Currently used as a gemstone (Jasper/agate variety), in construction aggregate, and by mineral collectors.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most vital resources for early humans to create sharp-edged tools like arrowheads and scrapers due to its predictable conchoidal fracture.

Field identification & locations

Identify by its 'waxy' or 'greasy' feel on smooth surfaces, high hardness, and curved (shell-like) fracture patterns. Frequently found in riverbeds, glacial Till, or eroding out of limestone cliffs.