sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 Mohs; Color: Tan to yellowish-brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (Microcrystalline quartz); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Tan to yellowish-brown
Luster: Waxy to dull

Identified June 22, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Tan to yellowish-brown; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (Microcrystalline quartz); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of silica-rich microfossils like diatoms or radiolarians, or through chemical precipitation in marine environments. This specimen shows significant rounding from water erosion, likely being a river pebble.

Uses & applications

Used historically for stone tools (arrowheads). Industrially used as a silica source, in glassmaking, or as a sturdy road aggregate.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, which is why it was historically used in flintlock firearms and for starting fires.

Field identification & locations

Identify in the field by its smooth, waxy texture and shell-like (conchoidal) fractures. It is commonly found in riverbeds, glacial tills, or as nodules within limestone or chalk formations.