sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: Grey, white, tan, or yellowish; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8.

Hardness: 7 on Mohs scale
Color: Grey, white, tan, or yellowish
Luster: Waxy to dull

Identified June 21, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grey, white, tan, or yellowish; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8.

Formation & geological history

Formed primarily through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. It can occur as nodules in limestone or as bedded deposits.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Today used as a component in construction aggregate, road surfacing, and occasionally as a gemstone in the form of flint or jasper.

Geological facts

Chert is essentially a biological graveyard of microscopic marine organisms. It was one of the most important minerals for early humans because of its ability to hold an extremely sharp edge.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy appearance, and characteristic shell-like (conchoidal) fracture pattern. Commonly found in sedimentary basins or as rounded pebbles in stream beds.