# Magnetite

**Magnetite** is an iron oxide mineral with the formula Fe²⁺Fe³⁺₂O₄, often shortened to Fe₃O₄, and it is the most strongly magnetic naturally occurring mineral as well as one of the two principal ores of iron, alongside hematite (Fe₂O₃).<sup>[1](https://www.mindat.org/show.php?id=2538&ld=1)</sup><sup> • </sup><sup>[2](https://www.mineralogist.org/m/magnetite)</sup> It crystallizes in the cubic system as a member of the spinel group, typically forming black octahedral crystals, and it was originally called lodestone, a name in use as early as 1548, before being named in 1845 by Wilhelm Karl von Haidinger for the locality at Magnesia, Greece.<sup>[1](https://www.mindat.org/show.php?id=2538&ld=1)</sup>

| Key fact | Detail |
|---|---|
| Formula | Fe²⁺Fe³⁺₂O₄ (Fe₃O₄); 72.36–72.4% iron by mass<sup>[1](https://www.mindat.org/show.php?id=2538&ld=1)</sup><sup> • </sup><sup>[3](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Magnetite)</sup> |
| Crystal data | Cubic, spinel group, space group Fd3̄m; typically octahedral crystals to 25 cm<sup>[4](https://www.handbookofmineralogy.org/pdfs/magnetite.pdf)</sup> |
| Physical properties | Hardness 5.5–6.5; specific gravity 5.175 measured; black color and streak; metallic to submetallic luster; strongly magnetic<sup>[1](https://www.mindat.org/show.php?id=2538&ld=1)</sup><sup> • </sup><sup>[4](https://www.handbookofmineralogy.org/pdfs/magnetite.pdf)</sup> |
| Magnetism | Ferrimagnetic below the Curie temperature T_C ≈ 850 K (580 °C)<sup>[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC9261838/)</sup><sup> • </sup><sup>[6](https://agupubs.onlinelibrary.wiley.com/doi/10.1002/jgrb.50291)</sup> |
| Verwey transition | At T_V ≈ 120–125 K the structure distorts from cubic to monoclinic and conductivity drops abruptly<sup>[7](https://www.nature.com/articles/nmat2084)</sup><sup> • </sup><sup>[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC9261838/)</sup> |
| Ore role | Principal iron ore with hematite; iron ore is almost always iron oxide, and 98% of iron ore is used in steelmaking<sup>[8](https://www.usgs.gov/centers/national-minerals-information-center/iron-ore-statistics-and-information)</sup> |
| Occurrence | Common accessory mineral in igneous and metamorphic rocks; extensive deposits in sedimentary banded iron formations<sup>[4](https://www.handbookofmineralogy.org/pdfs/magnetite.pdf)</sup> |

## Structure and magnetism

Magnetite is an inverse spinel. Oxygen ions form a cubic close-packed framework with tetrahedral A sites and octahedral B sites; half of the Fe³⁺ ions occupy tetrahedral sites, while the remaining Fe³⁺ and all of the Fe²⁺ occupy octahedral sites, giving the distribution Fe³⁺[Fe²⁺Fe³⁺]O₄.<sup>[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC9261838/)</sup><sup> • </sup><sup>[9](https://www.ak-guetlich.chemie.uni-mainz.de/files/2018/09/Moessbauer_Lectures_.pdf)</sup> The Fe³⁺ spins on the two sublattices align antiparallel and cancel, so the net magnetization comes from the Fe²⁺ ions on the octahedral B sites; this sublattice imbalance is ferrimagnetism, a state historically mistaken for ferromagnetism.<sup>[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC9261838/)</sup><sup> • </sup><sup>[10](https://core.ac.uk/download/pdf/1861011.pdf)</sup> Rapid hopping of the extra electron between Fe²⁺ and Fe³⁺ on B sites makes magnetite one of the few minerals that conducts electricity at room temperature.<sup>[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC9261838/)</sup><sup> • </sup><sup>[2](https://www.mineralogist.org/m/magnetite)</sup>

**The Verwey transition.** In 1939 Verwey found that bulk magnetite undergoes a transition near 120 K from a high-temperature conducting phase to a low-temperature insulating phase, with resistivity increasing abruptly by about two orders of magnitude and the structure changing from cubic to monoclinic.<sup>[7](https://www.nature.com/articles/nmat2084)</sup><sup> • </sup><sup>[11](https://www.sciencedirect.com/science/article/abs/pii/S1293255800010839)</sup> The low-temperature ground state, unresolved for over 70 years, was determined by high-energy microcrystal [X-ray diffraction](https://www.edgepedia.org/x-ray-diffraction): it is Fe²⁺/Fe³⁺ charge ordered and Fe²⁺ orbital ordered, with electrons localized in three-Fe "trimeron" units, in an acentric structure containing 168 frozen phonon modes.<sup>[12](https://www.jstage.jst.go.jp/article/jjspm/61/S1/61_S43/_article)</sup> In natural samples the transition temperature varies with stoichiometry and cation substitution: a survey of 1,110 samples showed a sharp peak at 118–120 K and a broad lower-temperature tail to about 80 K, with biogenic magnetite from magnetotactic bacteria having the lowest modal value of 100 K.<sup>[13](https://academic.oup.com/gji/article/224/2/1314/5942662)</sup> Cation vacancies and oxidation lower T_V, and the transition disappears above about 1.2% vacancy content.<sup>[14](https://www.sciencedirect.com/science/article/abs/pii/S0012821X06006510)</sup>

## Occurrence and ore geology

Magnetite is a common accessory mineral in igneous and metamorphic rocks, in which magmatic segregation or contact metamorphism can produce economic deposits, and it forms extensive deposits in sedimentary banded iron formations.<sup>[4](https://www.handbookofmineralogy.org/pdfs/magnetite.pdf)</sup> In [banded iron formations](https://www.edgepedia.org/banded-iron-formation), magnetite was chemically precipitated from seawater rich in dissolved ferrous iron before free oxygen built up in the oceans.<sup>[15](https://pubs.usgs.gov/bul/1924/report.pdf)</sup> Hydrothermal fluids also deposit magnetite in skarns, veins, and porphyry systems, and its composition records the conditions of formation: temperature, fluid composition, oxygen and sulfur fugacity, and host-rock buffering govern which trace elements enter the lattice.<sup>[16](https://www.usgs.gov/publications/chemistry-hydrothermal-magnetite-a-review)</sup>

**Trace-element fingerprinting.** The main discriminator elements are Mg, Al, Ti, V, Cr, Mn, Co, Ni, Zn, and Ga, commonly present at 10 to over 1,000 ppm with systematic variations between settings.<sup>[16](https://www.usgs.gov/publications/chemistry-hydrothermal-magnetite-a-review)</sup> [Discriminant](https://www.edgepedia.org/discriminant) plots such as Ni/(Cr + Mn) versus Ti + V and Ti/V separate hydrothermal from igneous magnetite and fingerprint different ore deposit types; for example, banded iron formation magnetite is low in most trace elements, while porphyry magnetite is high in Ti and V.<sup>[16](https://www.usgs.gov/publications/chemistry-hydrothermal-magnetite-a-review)</sup> This makes magnetite useful as a petrogenetic indicator and as a pathfinder in mineral exploration.<sup>[16](https://www.usgs.gov/publications/chemistry-hydrothermal-magnetite-a-review)</sup>

Because magnetite is dense and magnetic, iron formations produce strong geophysical signatures: their magnetic response is usually one to two orders of magnitude greater than that of the host rock, which aids aeromagnetic exploration.<sup>[17](https://pubs.usgs.gov/sir/2016/5089/a/sir20165089a.pdf)</sup>

## Mining and processing

Magnetite's strong magnetism is the basis of its beneficiation. On the [Mesabi Range](https://www.edgepedia.org/mesabi-range) in Minnesota, the high-grade hematite "natural ores" mined from 1890 to about 1980, totaling 2.5 billion tons, were largely depleted, and mining shifted to taconite, a hard, dense rock containing silicates and magnetite with about 25–30% iron content.<sup>[18](https://eros.usgs.gov/earthshots/taconite)</sup> The taconite is crushed to a fine powder, the magnetite is separated with magnets, and the concentrate is agglomerated into marble-sized pellets containing over 65% iron for shipment to steel mills.<sup>[18](https://eros.usgs.gov/earthshots/taconite)</sup> [Concentration](https://www.edgepedia.org/concentration) of roughly 3 tons of crude magnetic taconite, about 22% iron as magnetite, into 1 ton of pellets raises the iron content.<sup>[19](https://pubs.usgs.gov/bul/1082c/report.pdf)</sup>

## Oxidation and alteration

Magnetite oxidizes to maghemite (γ-Fe₂O₃) or hematite. Fine magnetite nanoparticles left in air at room temperature oxidize to maghemite, which is why maghemite is often substituted for magnetite in applications requiring stable storage.<sup>[20](https://pmc.ncbi.nlm.nih.gov/articles/PMC9820855/)</sup><sup> • </sup><sup>[21](https://www.mdpi.com/2312-7481/9/5/119)</sup> [Partial oxidation](https://www.edgepedia.org/partial-oxidation) produces particles with magnetite cores and maghemite shells whose coercivity exceeds that of either phase because of lattice strain at the interface.<sup>[22](https://www.cambridge.org/core/books/abs/mineral-magnetism/irontitanium-oxides/C436B1802EE2EE050F4C55C1A81D780D)</sup> The redox-related alteration of magnetite to hematite, called martitization, is a recognized feature of ore deposits.<sup>[16](https://www.usgs.gov/publications/chemistry-hydrothermal-magnetite-a-review)</sup>

## Biology and applied uses

Magnetotactic bacteria biomineralize magnetite in organelles called magnetosomes, nano-sized crystals enveloped by a lipid bilayer membrane and usually arranged in chains, which make the cells behave like motile compass needles aligned with [Earth's magnetic field](https://www.edgepedia.org/earths-magnetic-field).<sup>[23](https://pmc.ncbi.nlm.nih.gov/articles/PMC3811606/)</sup> The bacteria regulate crystal size and shape tightly, producing stable single-domain crystals with narrow size distributions.<sup>[24](https://pubmed.ncbi.nlm.nih.gov/34723168/)</sup>

**Water treatment.** Magnetite's combination of adsorption capacity and magnetic response solves the problem of separating fine loaded particles from treated water: a CSIRO process uses magnetite as a magnetic reagent for clarifying low-quality ground and surface waters, with plants in operation or under construction in Australia, the United Kingdom, and Taiwan, and the method has been extended to heavy-metal removal from tailings dams and to sewage treatment.<sup>[25](https://pubmed.ncbi.nlm.nih.gov/24233933/)</sup> Magnetite nanoparticles are also widely studied as adsorbents for dyes, heavy metals, and other pollutants, where high surface area, [superparamagnetism](https://www.edgepedia.org/superparamagnetism), and ease of functionalization allow magnetic recovery after treatment.<sup>[26](https://www.sciencedirect.com/science/article/pii/S2211715624000845)</sup>

## References

1. [Magnetite: Mineral information, data and localities, Mindat](https://www.mindat.org/show.php?id=2538&ld=1)
2. [Magnetite Properties, Formula & Mineral Information, Mineralogist.org](https://www.mineralogist.org/m/magnetite)
3. [Magnetite, 1911 Encyclopædia Britannica, Wikisource](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Magnetite)
4. [Magnetite, Handbook of Mineralogy, Mineralogical Society of America](https://www.handbookofmineralogy.org/pdfs/magnetite.pdf)
5. [Magnetism and the Trimeron Bond, Chemistry of Materials (2022)](https://pmc.ncbi.nlm.nih.gov/articles/PMC9261838/)
6. [Origin of two Verwey transitions, Chesapeake Bay impact structure, JGR Solid Earth (2013)](https://agupubs.onlinelibrary.wiley.com/doi/10.1002/jgrb.50291)
7. [Electrically driven phase transition in magnetite nanostructures, Nature Materials (2008)](https://www.nature.com/articles/nmat2084)
8. [Iron Ore Statistics and Information, U.S. Geological Survey](https://www.usgs.gov/centers/national-minerals-information-center/iron-ore-statistics-and-information)
9. [Mössbauer Lectures, University of Mainz](https://www.ak-guetlich.chemie.uni-mainz.de/files/2018/09/Moessbauer_Lectures_.pdf)
10. [Declaration (ferrimagnetism of magnetite), CORE](https://core.ac.uk/download/pdf/1861011.pdf)
11. [Possible influence of electron–lattice interactions on the Verwey transition, ScienceDirect](https://www.sciencedirect.com/science/article/abs/pii/S1293255800010839)
12. [The Verwey Phase of Magnetite: A Long-Running Mystery in Ferrites, J. Japan Soc. Powder Powder Metallurgy](https://www.jstage.jst.go.jp/article/jjspm/61/S1/61_S43/_article)
13. [On the distribution of Verwey transition temperatures in natural magnetites, Geophysical Journal International (2021)](https://academic.oup.com/gji/article/224/2/1314/5942662)
14. [Origin and implications of two Verwey transitions, Vredefort crater, Earth and Planetary Science Letters](https://www.sciencedirect.com/science/article/abs/pii/S0012821X06006510)
15. [Magnetite banded iron-formations, USGS Bulletin 1924](https://pubs.usgs.gov/bul/1924/report.pdf)
16. [The chemistry of hydrothermal magnetite: a review, USGS / Ore Geology Reviews (2014)](https://www.usgs.gov/publications/chemistry-hydrothermal-magnetite-a-review)
17. [USGS Mineral-Resource Assessment of the Sagebrush Focal Areas, SIR 2016-5089-A](https://pubs.usgs.gov/sir/2016/5089/a/sir20165089a.pdf)
18. [Taconite, USGS EROS Earthshots](https://eros.usgs.gov/earthshots/taconite)
19. [Iron-Ore Resources of the United States, 1955, USGS Bulletin 1082-C](https://pubs.usgs.gov/bul/1082c/report.pdf)
20. [Iron Oxide Nanoparticles: Compounds, Properties and Biological Applications, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC9820855/)
21. [Diversity of Iron Oxides: Mechanisms of Formation, Physical Properties and Applications, MDPI (2023)](https://www.mdpi.com/2312-7481/9/5/119)
22. [The Iron–Titanium Oxides, Mineral Magnetism, Cambridge University Press](https://www.cambridge.org/core/books/abs/mineral-magnetism/irontitanium-oxides/C436B1802EE2EE050F4C55C1A81D780D)
23. [Ecology, Diversity, and Evolution of Magnetotactic Bacteria, PMC (2013)](https://pmc.ncbi.nlm.nih.gov/articles/PMC3811606/)
24. [Current view of iron biomineralization in magnetotactic bacteria, PubMed (2021)](https://pubmed.ncbi.nlm.nih.gov/34723168/)
25. [Water purification with magnetic particles, Environmental Monitoring and Assessment (1991)](https://pubmed.ncbi.nlm.nih.gov/24233933/)
26. [State of the art on magnetic iron oxide nanoparticles in wastewater treatment, Results in Chemistry (2024)](https://www.sciencedirect.com/science/article/pii/S2211715624000845)

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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Elements and inorganic substances › Applied inorganic materials and minerals › Minerals, pigments, and applied inorganic materials › Anhydrous oxide minerals*

*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026; Oct 25, 2026 · Last review: Oct 15, 2026*

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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license