sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: brown, tan, gray; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: brown, tan, gray
Luster: waxy to dull

Identified July 13, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: brown, tan, gray; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. Microscopic silica replaces existing materials like limestone.

Uses & applications

Used historically for stone tools and starting fires; currently used in construction aggregate and as a collector's specimen.

Geological facts

Commonly known as flint when found in chalk or marly limestone. It was the primary material for prehistoric arrowheads and spear points due to its sharp edges when broken.

Field identification & locations

Identify by its waxy appearance, smooth conchoidal fracture (curved breaks), and extreme hardness (it will scratch glass). Commonly found in limestone beds or as nodules in riverbeds.