sedimentary

Chert (Flint)

Silicon dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Tan, brown, or dirty white; Luster: Waxy to dull pebble-like; Crystal Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.65

Hardness: 6
Color: Tan, brown, or dirty white
Luster: Waxy to dull pebble-like

Identified July 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or by chemical precipitation in marine environments, often replacing original limestone or chalk layers. This specimen appears water-worn or tumbled.

Uses & applications

Historically used for stone tools and weapons due to its sharp edges; currently used as construction aggregate, road metal, and occasionally for lapidary work.

Geological facts

Chert is a tough, durable rock that resists weathering better than the surrounding limestone it often forms in. It has been used by humans for millions of years to create fire (by sparking against steel) and sharp tools.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its characteristic conchoidal fracture which leaves smooth, curved surfaces when broken. It is extremely common in sedimentary riverbeds and gravel deposits worldwide.