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Depending on the environmental conditions present at the time of their formation, concretions can be created by either concentric or pervasive growth. [11] [12] In concentric growth, the concretion grows as successive layers of mineral precipitate around a central core. This process results in roughly spherical concretions that grow with time.
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.
Iron(III) oxide is a product of the oxidation of iron. It can be prepared in the laboratory by electrolyzing a solution of sodium bicarbonate, an inert electrolyte, with an iron anode: 4 Fe + 3 O 2 + 2 H 2 O → 4 FeO(OH) The resulting hydrated iron(III) oxide, written here as FeO(OH), dehydrates around 200 °C. [18] [19] 2 FeO(OH) → Fe 2 O 3 ...
Iron is stored in many organisms in the form of ferritin, which is a ferrous oxide encased in a solubilizing protein sheath. [ 10 ] Species of bacteria , including Shewanella oneidensis , Geobacter sulfurreducens and Geobacter metallireducens , use iron oxides as terminal electron acceptors .
Simplified diagram of the iron oxide cycle. For chemical reactions, the iron oxide cycle (Fe 3 O 4 /FeO) is the original two-step thermochemical cycle proposed for use for hydrogen production. [1] It is based on the reduction and subsequent oxidation of iron ions, particularly the reduction and oxidation between Fe 3+ and Fe 2+.
The Pierre Shale is the host formation for commercial petroleum deposits in the Florence and Canon City fields in Fremont County, Colorado, and the Boulder Oil Field in Boulder County, Colorado. More recently, natural gas has been extracted in the Raton Basin in southern Colorado .
Low-pressure phase diagram of pure iron. BCC is body centered cubic and FCC is face-centered cubic. Iron-carbon eutectic phase diagram, showing various forms of Fe x C y substances. Iron allotropes, showing the differences in structure. The alpha iron (α-Fe) is a body-centered cubic (BCC) and the gamma iron (γ-Fe) is a face-centered cubic (FCC).
Banded iron formation from the Barberton Greenstone Belt, South Africa. A typical banded iron formation consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe 3 O 4) or hematite (Fe 2 O 3), alternating with bands of iron-poor chert, often red in color, of similar thickness.