sedimentary

Chert (Flint)

Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: typically dark grey, black, or brown with waxy/greasy luster; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: typically dark grey, black, or brown with waxy/greasy luster

Identified March 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica in sedimentary rock layers or the replacement of carbonate material. Often found in limestone or chalk beds, frequently associated with Cretaceous period environments.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road construction as an aggregate, decorative landscaping, and occasionally for primitive technology replicas.

Geological facts

Flint was the primary material for the Stone Age tools that allowed early humans to hunt and process food. When struck against steel, it creates sparks due to the friction scraping off tiny particles of iron that spontaneously ignite.

Field identification & locations

Identify by its 'shell-like' (conchoidal) fracture patterns, extreme hardness (it will scratch glass), and waxy feel. Commonly found in riverbeds, chalk cliffs, and gravel deposits. Collectors look for unique banding or 'nodule' shapes.