sedimentary

Chert (variously known as Flint)

Microcrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown with a white chalky cortex; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown with a white chalky cortex
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments, often replacing carbonate minerals in limestone.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, as a filler in cement, and as 'flint' in fire-starting kits.

Geological facts

Chert is so hard it can scratch glass and produces sparks when struck against steel. It was the primary material for the 'Stone Age' technological revolution.

Field identification & locations

Identify by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch steel. Often found as nodules within limestone or chalk beds.