sedimentary

Flint / Chert

Silicon Dioxide (SiO2)

Hardness of 7 on the Mohs scale, typically gray, brown, or black in color, waxy to vitreous luster, microcrystalline or cryptocrystalline quartz structure, conchoidal fracture with no true cleavage, and a specific gravity of 2.60 to 2.65.

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments as a chemical sedimentary rock, commonly replacing calcium carbonate in limestone or chalk through the precipitation of silica-rich solutions or the accumulation of siliceous skeletal remains of microscopic organisms over millions of years.

Uses & applications

Historically used extensively for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture; later used for fire-striking flintlocks and currently used in abrasives and decorative landscaping.

Geological facts

Flint and chert are fundamentally the same material, though 'flint' is often used specifically for varieties found in chalk formations. The small hole visible in this specimen is often a fossil trace or a weathered-out inclusion.

Field identification & locations

Can be identified in the field by its distinctive conchoidal fracture (smooth, curved breakage patterns), high hardness that easily scratches glass, and waxy luster. Commonly found worldwide within limestone and chalk deposits.