sedimentary
Chert (with Limestone matrix)
Silicon dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: dirty tan, brown, black; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, conchoidal fracture
- Hardness
- 7 on Mohs scale
- Color
- dirty tan, brown, black
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: dirty tan, brown, black; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, conchoidal fracture
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments, often replacing calcium carbonate in limestone.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate and as a collector's specimen.
Geological facts
Chert is extremely durable and chemical resistant; its sharp edges when broken made it one of the most important minerals for early human survival through tool-making.
Field identification & locations
Identify by its ability to scratch glass and its smooth, shell-like (conchoidal) fracture surfaces. Common in riverbeds and limestone outcrops.
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