sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Gray to black; Luster: Waxy to dull; Breakdown: Conchoidal fracture; Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Gray to black
Luster: Waxy to dull

Identified July 6, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Gray to black; Luster: Waxy to dull; Breakdown: Conchoidal fracture; Specific Gravity: 2.65

Formation & geological history

Formed by the precipitation of silica in sedimentary environments often from the remains of siliceous organisms like radiolaria or diatoms. It occurs as nodules or layers in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers); currently used as a decorative stone, in construction aggregate, or as a fire-starting striking stone.

Geological facts

Flint is a dark variety of chert. Because it fractures with extremely sharp edges, it was the primary material for tool-making in the Stone Age. It is chemically very stable and resistant to weathering.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. It often has a waxy appearance and can be found in stream beds or within limestone outcrops.