sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Ranges from tan, brown, and gray to white; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Ranges from tan, brown, and gray to white
Luster: Waxy to dull

Identified April 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Often found as nodules or layers.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) and strike-a-lights; currently used in road surfacing, decorative landscaping, and occasionally as semi-precious gemstones when colorful (jasper/agate).

Geological facts

Chert has a conchoidal fracture, meaning it breaks with smooth, curved surfaces similar to glass, which allows it to be knapped into extremely sharp edges. It is one of the most durable sedimentary rocks.

Field identification & locations

Identify by its waxy texture, inability to be scratched by steel, and 'shell-like' curved breaks. It is commonly found in limestone outcrops or as smooth river pebbles. A critical material for prehistoric archaeology.