sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale. Color: Brown, tan, or gray. Luster: Waxy or dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Hardness: 7 Mohs scale
Color: Brown, tan, or gray
Luster: Waxy or dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale. Color: Brown, tan, or gray. Luster: Waxy or dull. Crystal Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Formation & geological history

Formed primarily by the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Often found in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Modern uses include road surfacing, flintlocks for firearms, and decorative lapidary work.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. When struck against steel, it produces sparks, making it essential for fire-lighting throughout human history.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture, sharp edges, and hardness (it will scratch glass). Commonly found in stream beds or eroding out of limestone outcrops.