sedimentary
Sandstone Concretion
Carbonate-cemented Sandstone Concretion
Hardness: 6-7 (approximate), Color: Tan to reddish-brown, Luster: Dull/Earthy, Crystal Structure: Granular/Amorphous, Texture: Coarse sand-like exterior, Shape: Spherical to sub-spherical
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Physical properties
Hardness: 6-7 (approximate), Color: Tan to reddish-brown, Luster: Dull/Earthy, Crystal Structure: Granular/Amorphous, Texture: Coarse sand-like exterior, Shape: Spherical to sub-spherical
Formation & geological history
Formed by the precipitation of mineral cement within the spaces between sediment grains, often around a nucleus like a leaf, shell, or bone. These typically form in sedimentary basins over millions of years as groundwater mineralizes.
Uses & applications
Primarily used as geological curiosities, educational specimens, or garden ornaments. Some large ones are tourist attractions.
Geological facts
Often mistaken for dinosaur eggs or cannonballs due to their near-perfect spherical shape. The 'Moqui Marbles' in Utah are a famous variety of small iron oxide concretions.
Field identification & locations
Identify by looking for spherical shapes that differ in hardness and color from the surrounding host rock. They are commonly found in eroding sandstone bluffs or riverbeds.
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