sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, white, and translucent smoky patterns; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, white, and translucent smoky patterns
Luster: Dull to waxy

Identified March 15, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, white, and translucent smoky patterns; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed by the precipitation of silica from groundwater in sedimentary environments, often replacing organic material or occupying voids in limestone. This specimen likely dates from the Cretaceous to the Jurassic periods.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and starting fires. Modern use includes road aggregate, glass manufacturing, and semi-precious jewelry components.

Geological facts

Chert is so hard it can scratch steel. When struck against iron or steel, it produces a spark, which led to its extensive use in flintlock firearms and early survival tools.

Field identification & locations

Identify by its 'conchoidal' (shell-like) fracture patterns and sharp edges. It is commonly found in riverbeds, limestone outcrops, and coastal chalk deposits. To identify in the field, look for a smooth, waxy surface that feels significantly harder than surrounding limestone.