sedimentary
Siltstone Concretion
Carbonate-cemented Siltstone Concretion
AI-generated identification · may be incorrectHardness: 3-5 (Mohs), Color: Tan to reddish-brown, Luster: Dull/Earthy, Crystal Structure: Microcrystalline, Cleavage: None, Shape: Spheroidal/Coiled
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Physical properties
Hardness: 3-5 (Mohs), Color: Tan to reddish-brown, Luster: Dull/Earthy, Crystal Structure: Microcrystalline, Cleavage: None, Shape: Spheroidal/Coiled
Formation & geological history
Formed by the precipitation of mineral cement within the spaces between sediment grains (silt or sand) around a nucleus, often during early diagenesis in sedimentary basins.
Uses & applications
Geological study, landscape decoration, and collecting; small ones are sometimes used as curiosities.
Geological facts
These often take on biomorphic or 'fossil-like' shapes, leading people to mistake them for dinosaur eggs, internal casts of seashells (steinkerns), or even petrified droppings.
Field identification & locations
Identified by their rounded, often bulbous or layered spherical shapes and different texture/hardness than the surrounding host rock. Commonly found in eroded shale or siltstone beds.
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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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Sandstone or Siltstone
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Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
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Sandstone
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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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