sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, greenish-gray, brown, or dull beige; Luster: Waxy, dull, or earthy; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5–2.8

Hardness: 7 on Mohs scale
Color: Gray, greenish-gray, brown, or dull beige
Luster: Waxy, dull, or earthy

Identified July 26, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, greenish-gray, brown, or dull beige; Luster: Waxy, dull, or earthy; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5–2.8

Formation & geological history

Formed via precipitation of silica-rich solutions or from accumulated siliceous microfossils (like radiolarians and diatoms) in marine sedimentary environments, which later recrystallize into microcrystalline quartz.

Uses & applications

Historically used by indigenous peoples for making sharp tools and arrowheads due to its conchoidal fracturing. Modern uses include road aggregate, landscape stone, and occasionally lapidary tumbling.

Geological facts

Chert spark-striking ability made it vital for flintlock firearms and early fire-starting techniques. Flint is a dark, high-purity variety of chert.

Field identification & locations

Identified by its high hardness (scratches glass), smooth waxy texture, and sharp shell-like (conchoidal) fracture edges. Found widely in limestone and chalk formations globally.