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Some examples of minerals in iron-rich rocks containing oxides are limonite, hematite, and magnetite. An example of a mineral in iron-rich rock containing carbonates is siderite and an example of minerals in an iron-rich rock containing silicate is chamosite. [2] They are often interbedded with limestones, shales, and fine-grained sandstones.
Ironstone (sandstone with iron oxides) from the Mississippian Breathitt Formation, Mile Marker 166, I-64, Kentucky. Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of an iron ore compound from which iron (Fe) can be smelted commercially.
Banded iron formation – Distinctive layered units of iron-rich sedimentary rock that are almost always of Precambrian age Breccia – Rock composed of angular fragments Calcarenite – Type of limestone that is composed predominantly of sand-size grains
Iron-rich sedimentary rocks are composed of >15% iron; the most common forms are banded iron formations and ironstones. [ 6 ] Phosphatic sedimentary rocks are composed of phosphate minerals and contain more than 6.5% phosphorus ; examples include deposits of phosphate nodules , bone beds, and phosphatic mudrocks.
Banded iron formations (BIFs; also called banded ironstone formations) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness and extend laterally for several hundred kilometers.
Iron oxides are derived from mafic igneous rocks and other iron-rich rocks; bauxites are derived from granitic igneous rock and other iron-poor rocks. [15] Nickel laterites occur in zones of the earth which experienced prolonged tropical weathering of ultramafic rocks containing the ferro-magnesian minerals olivine, pyroxene, and amphibole. [10]: 3
Taconite (/ ˈ t æ k ən aɪ t /) is a variety of banded iron formation, an iron-bearing (over 15% iron) sedimentary rock, in which the iron minerals are interlayered with quartz, chert, or carbonate.
This iron then precipitated out and deposited on the ocean floor. The banding is thought to be a result of changing plankton population. [38] [39] Sediment Hosted Copper forms from the precipitation of a copper rich oxidized brine into sedimentary rocks. These are a source of copper primarily in the form of copper-sulfide minerals. [40] [41]