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When the iron-bearing groundwater came into contact with more oxygen-rich groundwater, the reduced iron was converted back to insoluble iron oxide, which formed the concretions. [74] [75] [76] It is possible that reduced iron first formed siderite concretions that were subsequently oxidized. Iron-oxidizing bacteria may have played a role. [77]
The fossiliferous concretions are found in the Mazon River area of Grundy, Will, Kankakee, and Livingston counties. Additional fossils are found in LaSalle County, Illinois; between the Vermilion River and Marseilles, Illinois. The ironstone concretions are recovered from exposures along streams, roadcuts and in active or abandoned coal mine areas.
Nodule is also used for widely scattered concretionary lumps of manganese, cobalt, iron, and nickel found on the floors of the world's oceans. This is especially true of manganese nodules. Manganese and phosphorite nodules form on the seafloor and are syndepositional in origin. Thus, technically speaking, they are concretions instead of nodules ...
Similar to the marine nodules, concretion layers are defined based on iron and manganese content as well as their combination. [2] High iron content nodules appear a red or brown color, while high manganese content appears black or grey. [2] The dominant metal oxide is related to the elements enriched in the nodule.
The surface of these spherical concretions can range from being very rough to quite smooth. Some of the concretions are grooved spheres with ridges around their circumference. [5] [6] The abundant concretions found in the Navajo Sandstone consist of sandstone cemented together by hematite (Fe 2 O 3), and goethite (FeOOH).
Ferrous metals such as cast and wrought iron and steel usually corrode to form thick concretions that can entirely cover the metal object. [9] Corroded shipwreck artifacts that are made of iron may be conserved via electrolysis. Electrolysis is a method that uses an electric current to create a chemical reaction that cleans the object and ...
They described it as a dark-gray shale, fossiliferous, with veins and seams of gypsum, and concretions of iron oxide. The Pierre Shale is about 3,138 feet (956m) thick at the type locality. It overlies the Niobrara division and underlies the Fox Hills beds. [1] It was named for an occurrence near Fort Pierre on the Missouri River in South ...
Iron formations can be divided into subdivisions known as: banded iron formations (BIFs) and granular iron formations (GIFs). [ 3 ] The above classification scheme is the most commonly used and accepted, though sometimes an older system is used which divides iron-rich sedimentary rocks into three categories: bog iron deposits , ironstones , and ...