sedimentary

Chert (with Quartz veins)

Chert (Microcrystalline Silica, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray to black with white veins; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray to black with white veins
Luster: Waxy to dull

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray to black with white veins; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) in deep-sea environments or by chemical precipitation. The white veins are later quartz infillings of fractures.

Uses & applications

Used historically for stone tools due to its sharp edges; currently used in construction aggregate, road surfacing, and as decorative river stones.

Geological facts

Chert is so hard it can scratch steel and was often used alongside steel as a 'firestone'. It is chemically identical to flint, but the name 'flint' is usually reserved for specimens found in chalk or marly limestone.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a knife) and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and coastal areas as rounded pebbles.