For this purpose, it is synthesized rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.

Under anaerobic conditions, ferrous hydroxide (Fe(OH)2) can be oxidized by water to form magnetite and molecular hydrogen.

This process is described by the Schikorr reaction: This works because crystalline magnetite (Fe3O4) is thermodynamically more stable than amorphous ferrous hydroxide (Fe(OH)2 ).

[8] A more efficient method of preparing magnetite without troublesome residues of sodium, is to use ammonia to promote chemical co-precipitation from the iron chlorides: first mix solutions of 0.1 M FeCl3·6H2O and FeCl2·4H2O with vigorous stirring at about 2000 rpm.

Heat the mix to 70 °C, then raise the speed of stirring to about 7500 rpm and quickly add a solution of NH4OH (10 volume %).

[12][13] Pigment quality Fe3O4, so called synthetic magnetite, can be prepared using processes that use industrial wastes, scrap iron or solutions containing iron salts (e.g. those produced as by-products in industrial processes such as the acid vat treatment (pickling) of steel): Reduction of Fe2O3 with hydrogen:[14][15] Reduction of Fe2O3 with CO:[16] Production of nano-particles can be performed chemically by taking for example mixtures of FeII and FeIII salts and mixing them with alkali to precipitate colloidal Fe3O4.

[17] Iron(II) carbonate can also be thermally decomposed into Iron(II,III):[18] Reduction of magnetite ore by CO in a blast furnace is used to produce iron as part of steel production process:[5] Controlled oxidation of Fe3O4 is used to produce brown pigment quality γ-Fe2O3 (maghemite):[19] More vigorous calcining (roasting in air) gives red pigment quality α-Fe2O3 (hematite):[19] Fe3O4 has a cubic inverse spinel group structure which consists of a cubic close packed array of oxide ions where all of the Fe2+ ions occupy half of the octahedral sites and the Fe3+ are split evenly across the remaining octahedral sites and the tetrahedral sites.

[28] Ferumoxytol, sold under the brand names Feraheme and Rienso, is an intravenous Fe3O4 preparation for treatment of anemia resulting from chronic kidney disease.

[24][30] Magnetite has been found as nano-crystals in magnetotactic bacteria (42–45 nm)[6] and in the beak tissue of homing pigeons.