sedimentary

Chert (also known as Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Brown, grey, tan; Luster: Waxy to dull; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); SG: 2.65

Hardness: 7 (Mohs scale)
Color: Brown, grey, tan
Luster: Waxy to dull

Identified June 14, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Brown, grey, tan; Luster: Waxy to dull; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); SG: 2.65

Formation & geological history

Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or by chemical precipitation of silica in groundwater within sedimentary host rocks. Common in ancient limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads/knives) due to sharp edges; currently used as a road surfacing material, in construction aggregate, and occasionally as decorative landscaping stone.

Geological facts

Flint is a variety of chert that has been used by humans for millions of years to start fires and make tools. It produces sparks when struck against steel. Many nodules contain internal cavities or fossils.

Field identification & locations

Identify by its extremely smooth, shell-like (conchoidal) fracture surfaces and its ability to easily scratch glass. Found in nodules or layers within sedimentary rock units like limestone.