sedimentary

Chert (Flint Nodules)

Microcrystalline silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brown, tan, or grey interior with white chalky cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 6
Color: Brown, tan, or grey interior with white chalky cortex
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through the replacement of calcium carbonate by silica-rich fluids. Often found as nodules within limestone or chalk beds from the Cretaceous period.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road construction, landscape gravel, and occasionally for lapidary work.

Geological facts

Flint was the primary material for human tools for over two million years. It creates sparks when struck against steel due to its hardness and friction, leading to its name "flint" from the Old English for "hard rock."

Field identification & locations

Identify by its extremely sharp edges when broken and its characteristic conchoidal (shell-like) fracture pattern. Commonly found in river beds or erosion sites near limestone deposits.