sedimentary
Chert
Microcrystalline quartz (SiO2)
Hardness: 7 on the Mohs scale. Color varies widely from white, grey, brown, to black. Luster is vitreous to waxy. Fracture is conchoidal.
- Hardness
- 7 on the Mohs scale
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Physical properties
Hardness: 7 on the Mohs scale. Color varies widely from white, grey, brown, to black. Luster is vitreous to waxy. Fracture is conchoidal.
Formation & geological history
Formed via the accumulation of siliceous skeletal remains of marine organisms like diatoms or radiolarians, or through the direct chemical precipitation of silica from aqueous solutions in sedimentary environments.
Uses & applications
Historically used by ancient humans for making stone tools, arrowheads, and blades due to its conchoidal fracture. Also used in abrasives, road aggregate, and historically for striking fire.
Geological facts
Chert that is dark or black is commonly referred to as flint. It is extremely durable and resists weathering better than surrounding carbonate rocks.
Field identification & locations
Can be identified in the field by its sharp edges when broken, high hardness (scratches glass), and waxy luster. Found worldwide in limestone and chalk formations.
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