sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Gray, brown, black, white, or green. Luster: Waxy to vitreous. Crystal structure: Microcrystalline/cryptocrystalline. Conchoidal fracture, no cleavage.
- Hardness
- 7 on the Mohs scale
- Color
- Gray, brown, black, white, or green
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on the Mohs scale. Color: Gray, brown, black, white, or green. Luster: Waxy to vitreous. Crystal structure: Microcrystalline/cryptocrystalline. Conchoidal fracture, no cleavage.
Formation & geological history
Formed via chemical precipitation from silica-rich solutions in marine environments or through the replacement of limestone or chalk by silica during diagenesis.
Uses & applications
Historically used for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used in construction aggregate and historically for starting fires when struck against steel.
Geological facts
Chert is extremely durable and weather-resistant, which is why ancient stone tools made from it survive exceptionally well in the archaeological record. Varieties include flint, jasper, and chalcedony.
Field identification & locations
Identify by its hardness (scratches glass), waxy luster, and characteristically sharp conchoidal fracture. Commonly found in limestone and chalk formations worldwide.
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