sedimentary
Concretion (Sandstone)
Carbonate-cemented Sandstone Concretion
Hardness: 3-5 (Mohs scale), Color: tan/beige to grey with dark specks, Luster: dull/earthy, Crystal structure: microcrystalline cement, Cleavage: none (fractures irregularly)
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Physical properties
Hardness: 3-5 (Mohs scale), Color: tan/beige to grey with dark specks, Luster: dull/earthy, Crystal structure: microcrystalline cement, Cleavage: none (fractures irregularly)
Formation & geological history
Formed through the precipitation of mineral cement (typically calcite or iron oxides) in the spaces between sediment grains, often around a nucleus like a leaf or shell. This occurs within sedimentary layers before they are fully deeply buried.
Uses & applications
Primarily used as decorative display pieces, geological curiosities, or for educational purposes. Large ones are used in landscaping.
Geological facts
Concretions are often mistaken for fossilized eggs, dinosaur bones, or even man-made artifacts like cannonballs due to their perfectly spherical shape.
Field identification & locations
Identify by their rounded, often spherical or disc-like shape that differs from the surrounding rock. Common in sandstone or shale formations. Look for a 'seed' or nucleus in the center if cracked open.
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