sedimentary

Chert

Chert (Silica: SiO2)

Hardness: 7 (Mohs scale); Color: light greyish-green to tan; Luster: dull to waxy; Crystal structure: cryptocrystalline silicon dioxide; Fracture: conchoidal (shell-like curves); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: light greyish-green to tan
Luster: dull to waxy

Identified July 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains of marine organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Found in sedimentary formations of various geological ages from Precambrian to recent.

Uses & applications

Historically used for stone tools/weapons due to conchoidal fracture. Modernly used as an ornamental stone, in construction aggregate, and as a raw material for spark-production (fire-starters).

Geological facts

Chert is a broad category that includes jasper and flint. It was one of the most important minerals for early humans because its sharp edges were used to create arrowheads, knives, and scrapers.

Field identification & locations

Identify by its extreme hardness (will scratch glass) and characteristic conchoidal fracture patterns. Commonly found in limestone or dolomite beds as nodules or layers. Look for smooth, curved breaks on the surface.