sedimentary
Concretion with Geode Cavity
Ferruginous Sandstone Concretion with Quartz Center
Hardness: 6-7 (quartz parts), Color: Reddish-brown, tan, and grey, Luster: Dull/earthy exterior with vitreous interior, Structure: Massive/concentric, Cleavage: None
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Physical properties
Hardness: 6-7 (quartz parts), Color: Reddish-brown, tan, and grey, Luster: Dull/earthy exterior with vitreous interior, Structure: Massive/concentric, Cleavage: None
Formation & geological history
Formed by the precipitation of mineral cement in the spaces between particles in sediment. Often found in seafloors or lakebeds where minerals like iron oxide or silica concentrate around a nucleus over millions of years.
Uses & applications
Primarily used for geological study, teaching, and as a decorative collector's specimen. Larger examples are used in landscaping.
Geological facts
The hole in the center suggests a possible 'hollow concretion' or a geode that has weathered open. These are sometimes mistaken for fossils or man-made artifacts because of their symmetrical shapes.
Field identification & locations
Look for rounded or oblong nodules that feel heavier than surrounding rocks. Often found in eroding cliffs or stream beds. Breaking them open may reveal hollow centers lined with crystals.
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