sedimentary

Chert (Flint / Chalcedony variety)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Cream, tan, grey, brown, and reddish tones; Luster: Waxy to vitreous; Cleavage: None (conchoidal fracture); Specific gravity: ~2.65; Crystal system: Trigonal (microcrystalline).

Hardness: 7 on Mohs scale
Color: Cream, tan, grey, brown, and reddish tones
Luster: Waxy to vitreous

Identified July 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in sedimentary environments through the precipitation of silica from groundwater or accumulated siliceous skeletal remains (diatoms, radiolarians) in deep-sea sediments. It can also form as replacement nodules in limestone or chalk beds.

Uses & applications

Historically used for knapping arrowheads, spears, and flintlock ignition tools due to its sharp conchoidal edges. Modern uses include gemstone cabochons, lapidary projects, decorative specimens, and aggregate.

Geological facts

Chert and flint are among the earliest materials used by prehistoric humans to craft tools and start fires. When struck against iron or steel, chert creates sparks capable of igniting tinder.

Field identification & locations

Identified by its extreme hardness (scratches glass readily), smooth waxy feel, and sharp shell-like (conchoidal) fractures. Widely found worldwide in sedimentary rock formations, rivers, and gravel deposits.

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