sedimentary
Sandstone Concretion
Sedimentary Concretion (SiO2 or CaCO3 cemented)
Hardness: 6-7 (if silica-cemented); Color: Tan, brown, or reddish due to iron oxides; Luster: Dull, earthy; Crystal Structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.0-2.6
- Hardness
- 6-7 (if silica-cemented)
- Color
- Tan, brown, or reddish due to iron oxides
- Luster
- Dull, earthy
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Physical properties
Hardness: 6-7 (if silica-cemented); Color: Tan, brown, or reddish due to iron oxides; Luster: Dull, earthy; Crystal Structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.0-2.6
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.
Uses & applications
Used primarily for geological study, decorative landscaping, and occasionally as curiosities for collectors. Large, perfectly spherical ones are highly sought after.
Geological facts
Concretions are often mistaken for dinosaur eggs or fossils because of their rounded shape. They can range from a few millimeters to several meters in diameter.
Field identification & locations
Identify by its distinct rounded or nodular shape that differs from the surrounding bedding. Common in sandstone or shale formations. Look for concentric layering if the stone is broken.
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