[8] It forms in several types of environments, from freshwater to marine systems, aquifers to hydrothermal hot springs and scales, soils, and areas affected by mining.

It can be precipitated directly from oxygenated iron-rich aqueous solutions, or by bacteria either as a result of a metabolic activity or passive sorption of dissolved iron followed by nucleation reactions.

[22][23][24] A single phase model for both ferrihydrite and hydromaghemite[25] has been proposed by Michel et al.,[26][27] in 2007–2010, based on pair distribution function (PDF) analysis of x-ray total scattering data.

These properties confer a high ability to adsorb many environmentally important chemical species, including arsenic, lead, phosphate, and organic molecules (e.g., humic and fulvic acids).

[49] Under reducing conditions as those found in gley soils, or in deep environments depleted in oxygen, and often with the assistance of microbial activity, ferrihydrite can be transformed in green rust, a layered double hydroxide (LDH), also known as the mineral fougerite.