sedimentary

Chert (v. Flint)

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: tan, grey, or brownish-grey with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Color: tan, grey, or brownish-grey with waxy luster

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, grey, or brownish-grey with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & geological history

Formed by precipitation of silica from groundwater or the accumulation of silica-rich organic remains (like radiolarians or diatoms) in marine environments. Found in Paleozoic to Cenozoic sedimentary layers.

Uses & applications

Historically used for making stone tools (knapping) due to sharp edges. Today used in construction aggregate, road surfacing, and as a decorative stone in landscaping.

Geological facts

Because it breaks with a conchoidal fracture like glass, it creates edges sharper than a steel scalpel. Flint is a specific dark variety of chert often found in chalk or marly limestone.

Field identification & locations

Identify by its waxy look, hardness (it will scratch glass), and the way it breaks into curved, sharp flakes. Common in limestone outcrops and riverbeds.