sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: tan, brown, or grey with iron staining, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Identified July 20, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, brown, or grey with iron staining, Luster: waxy to dull, Structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater or marine environments. It is often found as nodules inside limestone or chalk formations.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges when broken. Today used as road aggregate, in landscaping, and as a material for lapidary tumbling.

Geological facts

Because it breaks with a conchoidal (shell-like) fracture producing razor-sharp edges, it was a vital survival resource for prehistoric humans. It is also known as flint when found in chalk.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its waxy texture, and its smooth, curved fracture surfaces. Commonly found in riverbeds, glacial till, and sedimentary outcrops.