sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 Mohs scale; Color: Beige, tan, or light gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); High specific gravity around 2.6

Hardness: 7 Mohs scale
Color: Beige, tan, or light gray
Luster: Dull to waxy

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Beige, tan, or light gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); High specific gravity around 2.6

Formation & geological history

Formed via the accumulation of siliceous oozes or through the replacement of calcium carbonate by silica in sedimentary basins. Most commonly found in limestone or chalk beds.

Uses & applications

Historically used for stone tools and arrowheads; currently used as road base, decorative landscaping stone, and as an industrial abrasive.

Geological facts

Chert has been used by humans for hundreds of thousands of years to create sharp-edged tools due to its conchoidal fracture pattern. Flint is a well-known dark variety of chert.

Field identification & locations

Identifiable by its extreme hardness (scratches glass), waxy feel, and smooth curved (conchoidal) breaks. Often found as nodules or layers within sedimentary rock outcrops.