<P> Banded iron formations (BIFs) were originally chemical muds and contain well developed thin lamination . They are able to have this lamination due to the lack of burrowers in the Precambrian . BIFs show regular alternating layers that are rich in iron and chert that range in thickness from a few millimeters to a few centimeters . The formation can continue uninterrupted for tens to hundreds of meters stratigraphically . These formations can contain sedimentary structures like cross-bedding, graded bedding, load casts, ripple marks, mud cracks, and erosion channels . In comparison to GIFs, BIFs contain a much larger spectrum of iron minerals, have more reduced facies, and are more abundant . </P> <P> Granular iron formations (GIFs) were originally well - sorted chemical sands . They lack even, continuous bedding that takes the form of discontinuous layers . Discontinuous layers likely represent bedforms that were generated by storm waves and currents . Any layers that are thicker than a few meters and are uninterrupted, are rare for GIFs . They contain sand - sized clasts and a finer grained matrix, and generally belong to the oxide or silicate mineral facies . </P> <P> Iron formations are sometimes divided into Raptian - type, Algoma - type and Superior - type . </P> <P> Algoma types are small lenticular iron deposits that are associated with volcanic rocks and turbidites . Iron content in this class type rarely exceeds 10 tons . They range in thickness from 10 - 100 meters . Deposition occurs in island arc / back arc basins and intracratonic rift zones . </P>

Metals are extracted from a mixture of rock soil and metallic mineral called