sedimentary

Chert / Microcrystalline Quartz

Chert (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Dark grey to charcoal, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Dark grey to charcoal, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific gravity: 2.6

Formation & geological history

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

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Currently used in road construction as aggregate and occasionally as a decorative landscape stone.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most vital resources for prehistoric humans, often traded over long distances. High-quality colorful varieties are known as Jasper.

Field identification & locations

Look for a smooth, waxy texture and shell-like (conchoidal) fractures. It will not react with acid (unlike limestone) and is often found as pods or layers within carbonate rocks.