sedimentary
Chert (containing Quartz)
Microcrystalline Silica (SiO2)
Hardness: 7 on the Mohs scale; Color: Grey, tan, and translucent white patches; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Grey, tan, and translucent white patches
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on the Mohs scale; Color: Grey, tan, and translucent white patches; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed by the precipitation of silica-rich fluids within sedimentary rock layers like limestone or through the accumulation of siliceous remains such as diatoms or radiolarians. Often found in Phanerozoic era strata.
Uses & applications
Historically used for stone tools (arrowheads) due to its sharp edges; modernly used as road aggregate, in glass manufacturing, and as a durable material for tumbling and craft jewelry.
Geological facts
Chert has a distinct sharp edge when broken, leading to its widespread use in prehistoric toolmaking. It is one of the most chemically stable and weather-resistant sedimentary rocks.
Field identification & locations
Identify in the field by its conchoidal (shell-like) fracture pattern and the fact that it can scratch glass easily. Commonly found in riverbeds, limestone outcroppings, and coastal gravels.
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