sedimentary
Chert
Microcrystalline quartz (SiO2)
AI-generated identification · may be incorrectHardness of 7 on the Mohs scale, earthy to waxy luster, conchoidal fracture, and colors ranging from white to dark brown or black.
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Physical properties
Hardness of 7 on the Mohs scale, earthy to waxy luster, conchoidal fracture, and colors ranging from white to dark brown or black.
Formation & geological history
Formed through the chemical precipitation of silica from seawater or the accumulation of siliceous skeletal remains of microscopic organisms over millions of years.
Uses & applications
Historically used by early humans for making stone tools and weapons due to its sharp conchoidal fracture; occasionally used as a decorative stone.
Geological facts
Chert is extremely durable and resistant to weathering, often surviving in the geological record long after surrounding limestone has eroded away.
Field identification & locations
Identify by its extreme hardness, waxy luster, and sharp edges when fractured; commonly found nodules within chalk or limestone formations worldwide.
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Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion
Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image
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Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone or Siltstone
Arenite (if sandstone)
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Sandstone
Arenite
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Shale
Shale (clastic sedimentary rock)
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Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
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