[3] Anhydrous ferric hydroxide occurs in the nature as the exceedingly rare mineral bernalite, Fe(OH)3·nH2O (n = 0.0–0.25).

Iron(III) oxyhydroxide is the main component of other minerals and mineraloids: The color of iron(III) oxyhydroxide ranges from yellow through dark-brown to black, depending on the degree of hydration, particle size and shape, and crystal structure.

[2] Limonite, a mixture of various hydrates and polymorphs of ferric oxyhydroxide, is one of the three major iron ores, having been used since at least 2500 BC.

[12] Thus the oxyhydroxide can be obtained in the lab by reacting an iron(III) salt, such as ferric chloride or ferric nitrate, with sodium hydroxide:[13] In fact, when dissolved in water, pure FeCl3 will hydrolyze to some extent, yielding the oxyhydroxide and making the solution acidic:[12] Therefore, the compound can also be obtained by the decomposition of acidic solutions of iron(III) chloride held near the boiling point for days or weeks:[14] (The same process applied to iron(III) nitrate Fe(NO3)3 or perchlorate Fe(ClO4)3 solutions yields instead particles of α-Fe2O3.

[15] The oxyhydroxide prepared from ferric chloride is usually the β polymorph (akaganeite), often in the form of thin needles.