sedimentary
Sandstone concretion
Arenite sedimentary rock (concretion/nodule)
Hardness: 6-7 (Mohs scale), Color: tan to reddish-brown (iron-stained), Luster: dull/earthy, Crystal structure: clastic (granular), Specific gravity: 2.2-2.8
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Physical properties
Hardness: 6-7 (Mohs scale), Color: tan to reddish-brown (iron-stained), Luster: dull/earthy, Crystal structure: clastic (granular), Specific gravity: 2.2-2.8
Formation & geological history
Formed by the precipitation of mineral cement (often calcite or iron oxide) within the spaces between sediment grains. This typically occurs in marine or terrestrial sedimentary basins over millions of years.
Uses & applications
Primarily of interest to collectors and geologists as curiosities; occasionally used in landscaping or as decorative garden stones.
Geological facts
Concretions are often mistaken for fossils, artifacts, or even meteorites because of their unusual rounded or biological-looking shapes. Some grow around a central nucleus like a pebble or fossil.
Field identification & locations
Identify in the field by its rounded or bulbous shape which differs from the surrounding bedding. Common in sandstone formations worldwide, especially in arid or coastal regions.
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