sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 6.5-7 (Mohs scale); Color: gray, tan, or white; Luster: dull to waxy; Texture: fine-grained/microcrystalline; Cleavage: none (conchoidal fracture).

Hardness: 6
Color: gray, tan, or white
Luster: dull to waxy

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: gray, tan, or white; Luster: dull to waxy; Texture: fine-grained/microcrystalline; Cleavage: none (conchoidal fracture).

Formation & geological history

Forms primarily as nodules or layers through the accumulation and precipitation of silica-rich marine microfossils (like radiolaria or diatoms) or by replacement of other minerals in sedimentary limestone.

Uses & applications

Historically used for stone tools (flint knapping) due to its sharp edges; used today as road fill, construction aggregate, and occasionally as an ornamental garden stone.

Geological facts

Flint is a dark variety of chert. Because of its hardness and conchoidal fracture, it was the primary material used by prehistoric humans to create spearheads, scrapers, and arrowheads.

Field identification & locations

Identified by its extreme hardness (scratches glass), waxy feel, and smooth, shell-like (conchoidal) breaks. Often found in gravel beds or embedded within limestone outcrops.