sedimentary

Chert (with Quartz veins)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Dark brown (liver-colored) with white veins; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Dark brown (liver-colored) with white veins
Luster: Waxy to dull

Identified June 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) or by chemical precipitation. The white veins are secondary quartz infilling fractures caused by tectonic stress.

Uses & applications

Used historically for stone tools due to its sharp edges; currently used as decorative gravel, in lapidary work as 'river stones', and for fire-striking.

Geological facts

Chert is so hard it can scratch steel. It is chemically identical to flint, but flint is usually found in chalk or marly limestone, whereas chert is found in many types of limestone. The white 'veins' are called 'septaria' when they form specific patterns.

Field identification & locations

Identify by its waxy appearance and smooth, curved (conchoidal) fractures. The white veins will not react to acid, distinguishing them from calcite. Common in riverbeds and glacial tills.