sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: White to tan with slight weathering, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: White to tan with slight weathering, Luster: Dull to waxy, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.65

Formation & geological history

Formed via the accumulation of silica-rich microfossils or inorganic precipitation in marine or groundwater environments. It typically forms within limestone or chalk beds as nodules or layers.

Uses & applications

Historically used for making stone tools (arrowheads). Modern uses include road surfacing materials, decorative landscaping, and as a raw material for ceramics and glass.

Geological facts

Chert is so hard it can strike sparks against steel. It was one of the most important minerals for prehistoric humans because it breaks into very sharp edges through conchoidal fracturing.

Field identification & locations

Identify by its high hardness (cannot be scratched by a steel knife), dull appearance, and smooth, shell-like (conchoidal) breaks. It is commonly found in sedimentary basins and riverbeds.