sedimentary

Chert (Flint Nodules)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs). Color: Gray, tan, white. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Gray, tan, white
Luster: Waxy to dull

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs). Color: Gray, tan, white. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture).

Formation & geological history

Forms in sedimentary environments, often through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation within limestone or chalk beds.

Uses & applications

Historically used for stone tools and starting fires (striking steel). Modernly used in construction aggregate and as a collector's specimen.

Geological facts

Flint is a variety of chert that occurs primarily in chalk and marly limestone. It was the primary material for spearheads and arrowheads in prehistoric times due to its sharp conchoidal edges.

Field identification & locations

Identify by its waxy luster, hardness (it will scratch glass), and its distinctive curved (conchoidal) fracture planes when broken. Often found in chalk cliffs or as river pebbles.