sedimentary

Chert (Siliceous Siltstone/Quartzite)

Silicon dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: reddish-brown with tan inclusions; Luster: dull to waxy; Structure: microcrystalline/cryptocrystalline; Fracture: conchoidal to sub-conchoidal; Specific Gravity: 2.6-2.7

Hardness: 6
Color: reddish-brown with tan inclusions
Luster: dull to waxy

Identified July 15, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: reddish-brown with tan inclusions; Luster: dull to waxy; Structure: microcrystalline/cryptocrystalline; Fracture: conchoidal to sub-conchoidal; Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the precipitation of silica from seawater or the replacement of limestone by silica-rich fluids. Likely originated in a marine sedimentary environment during various geological ages from the Precambrian to the Cenozoic.

Uses & applications

Used historically for stone tools due to its sharp edges when fractured. Modern uses include road aggregate, aquarium decor, and landscape gravel.

Geological facts

Chert is so hard that it can strike sparks against steel. It is chemically identical to quartz but has an extremely fine-grained structure that gives it a smooth, flint-like appearance.

Field identification & locations

Identify by its hardness (will scratch glass), conchoidal fracture patterns, and lack of visible grains. Commonly found in riverbeds or as nodules within limestone formations.