sedimentary
Concretion
Sedimentary concretion (Mineral aggregate, often carbonate-cemented)
AI-generated identification · may be incorrectHardness varies from 3 to 7 depending on cement; color ranges from brown to grey; dull luster; amorphous or microcrystalline structure.
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Physical properties
Hardness varies from 3 to 7 depending on cement; color ranges from brown to grey; dull luster; amorphous or microcrystalline structure.
Formation & geological history
Formed by the precipitation of mineral cement within the spaces between sediment grains, typically during burial diagenesis in sedimentary strata.
Uses & applications
Valued by fossil collectors as they frequently enclose well-preserved fossils, and used as decorative display specimens.
Geological facts
Concretions are often mistaken for meteorites or dinosaur eggs due to their unusual rounded shapes and distinctive weathering rinds.
Field identification & locations
Identify by their distinct spherical or discoidal shapes and hard outer shells compared to the surrounding host rock. Commonly found in shales and sandstones worldwide.
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Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
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