sedimentary
Chert (Siliceous Siltstone/Quartzite)
Silicon dioxide (SiO2)
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
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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.
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