sedimentary
Flint
SiO2 (Microcrystalline quartz / Chert)
AI-generated identification · may be incorrectHardness of 7 on the Mohs scale, dark grey to black color with a waxy to vitreous luster, conchoidal fracture, and cryptocrystalline structure.
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Physical properties
Hardness of 7 on the Mohs scale, dark grey to black color with a waxy to vitreous luster, conchoidal fracture, and cryptocrystalline structure.
Formation & geological history
Formed through the chemical replacement of calcium carbonate in limestone by silica-rich groundwaters during the Cretaceous period.
Uses & applications
Historically used for making stone tools, arrowheads, and fire-starting flint-locks; currently used in abrasives and occasionally as a decorative stone.
Geological facts
Flint produces sparks when struck against steel due to its high hardness and brittle fracture, making it essential for survival throughout human history.
Field identification & locations
Easily identified by its sharp conchoidal fracture edges and dark color; 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)
Sedimentary
Sandstone
Arenite
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Shale
Shale (clastic sedimentary rock)
sedimentary
Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
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