sedimentary

Chert / Flint

Microcrystalline Silica (SiO2)

Hardness: 7 (Mohs scale). Color: Dark grey, charcoal, or muddy brown with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.

Hardness: 7 (Mohs scale)
Color: Dark grey, charcoal, or muddy brown with waxy luster

Identified March 10, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale). Color: Dark grey, charcoal, or muddy brown with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.

Formation & geological history

Formed through the precipitation of silica from seawater or the accumulation of siliceous biological remains (diatoms/radiolarians) during the Paleozoic to Mesozoic eras. It typically forms as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and arrowheads; modernly used as a decorative stone in landscaping, a flux in ceramics, and to produce sparks for fire-starting.

Geological facts

Flint was the primary material for the 'Stone Age' because its conchoidal fracture creates edges sharper than a steel scalpel. It is also famous for its ability to create sparks when struck against steel.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is commonly found in riverbeds, glacial till, and embedded in chalk cliffs. Collectors look for unique banding or 'ghost' fossils within the mass.