sedimentary

Chert

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: gray, tan, or brown; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8

Hardness: 7 (Mohs scale)
Color: gray, tan, or brown
Luster: waxy to dull

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: gray, tan, or brown; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8

Formation & geological history

Formed by the accumulation of siliceous oozes on the seafloor or by the replacement of carbonate minerals in limestone or chalk beds. Often Paleozoic to Mesozoic in age.

Uses & applications

Historically used for stone tools (arrowheads). Modern uses include road surfacing, construction aggregate, and as a polishing media in rock tumblers.

Geological facts

Flint is a variety of chert. Because of its hardness and conchoidal fracture, it was one of the most important materials for early humans to create sharp cutting tools and fire-starters.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), waxy feel, and smooth, curved fracture surfaces. Commonly found in limestone outcrops or as rounded pebbles in riverbeds.