MAGNETITE

Magnetite is the most strongly magnetic of all naturally occurring minerals on Earth — a black, opaque, ferrimagnetic iron oxide mineral with chemical formula Fe₃O₄ (Fe²⁺Fe³⁺₂O₄), IMA symbol Mag, Strunz classification 4.BB.05, Dana classification 7.2.2.3, isometric crystal system (cubic), space group Fd3m (no. 227), unit cell a = 8.397 Å (Z = 8), Mohs hardness 5.5–6.5, specific gravity 5.17–5.18, and the diagnostic property of strong attraction to a magnet and remanent magnetisation (lodestone behaviour); it is a member of the spinel group with an inverse spinel structure in which O²⁻ ions form a face-centred cubic lattice, half the Fe³⁺ ions occupy tetrahedral sites, and the remaining Fe³⁺ plus all Fe²⁺ ions occupy octahedral sites.
Magnetite is one of the world's most important iron ore minerals, serving as a major feedstock for steelmaking (processed to pig iron or sponge iron in blast furnaces), as the precursor to the promoted iron catalyst for the Haber–Bosch nitrogen fixation process (consuming approximately 2–3% of the world's energy budget), and as the active phase in dense-medium coal separation, water-treatment magnetic separation, ferrofluids for targeted drug delivery and MRI contrast enhancement, and as a Curie temperature (580°C) reference material for paleomagnetism and geophysics.
Magnetite occurs widely in igneous, metamorphic, hydrothermal, and sedimentary environments including banded iron formations (BIFs), beach and river placers, skarns, porphyry deposits, and biomineralised magnetosomes in magnetotactic bacteria and animal tissues; it was formally named in 1845 by Wilhelm Karl von Haidinger for the locality at Magnesia, Greece, and is not classified as hazardous under GHS for bulk natural mineral handling.

Chemical Formula: Fe₃O₄
IMA Symbol: Mag
Strunz Classification: 4.BB.05
Dana Classification: 7.2.2.3
Molecular Weight: 231.53 g/mol

Synonyms: Iron(II,III) oxide, Ferrous ferric oxide, Ferrosoferric oxide, Lodestone (naturally magnetised variety), Magnetic iron ore, Fe₃O₄, Black iron oxide, Iron black, Magnetite-Mag, IMA symbol Mag, Strunz 4.BB.05

Composed of iron and oxygen, Magnetite has the chemical formula Fe₃O₄.
The alternative name iron(II,III) oxide reflects the mixed oxidation states present in Magnetite.

Both divalent Fe²⁺ and trivalent Fe³⁺ ions occur within the structure of Magnetite.
An inverse spinel crystal structure gives Magnetite its characteristic atomic arrangement.

In Magnetite, oxygen ions form a cubic close-packed framework around the iron ions.
Tetrahedral and octahedral sites accommodate the different iron ions found in Magnetite.

Black to brownish-black colours characterise most natural specimens of Magnetite.
Regardless of surface appearance, Magnetite normally produces a black streak.

Metallic to submetallic lustre gives crystalline Magnetite a distinctive appearance.
Octahedral and dodecahedral crystal habits commonly develop in well-formed Magnetite.

A Mohs hardness of approximately 5.5–6.5 makes Magnetite moderately hard.
With a specific gravity close to 5.2, Magnetite remains considerably denser than most common rock-forming minerals.

Among naturally occurring minerals, Magnetite displays exceptionally strong magnetic behaviour.
Ferrimagnetic ordering allows Magnetite to respond readily to external magnetic fields.

Naturally magnetised pieces of Magnetite are known as lodestone.
Early observations of lodestone made Magnetite important in the historical discovery of magnetism.

Igneous and metamorphic rocks commonly contain small grains of Magnetite.
Sedimentary deposits and banded iron formations can also host economically important Magnetite.

Crystallisation from magma may concentrate Magnetite in layered igneous intrusions.
Hydrothermal and metamorphic processes can redistribute Magnetite into veins and mineralised zones.

Certain magnetotactic bacteria produce microscopic crystals of Magnetite inside specialised structures called magnetosomes.
Chains of biological Magnetite crystals help these bacteria align with the Earth’s magnetic field.

The theoretical iron content of pure Magnetite reaches approximately 72.4% by weight.
High iron content makes Magnetite one of the principal raw materials for iron and steel production.

Magnetic separation can efficiently concentrate Magnetite from crushed ore.
The magnetic response of Magnetite simplifies recovery from many mineral-processing streams.

Concentrated Magnetite can be ground and formed into pellets for blast furnaces or direct-reduction processes.
Fine particle size and controlled chemistry improve the processing performance of Magnetite concentrates.

Dense-medium separation systems use Magnetite to control the density of the separation suspension.
Coal preparation, mineral beneficiation, and recycling operations benefit from the recoverability of Magnetite.

After separation, magnetic equipment can collect and recycle Magnetite from process slurries.
Repeated recovery makes Magnetite a practical medium for continuous density-separation circuits.

As a black inorganic pigment, Magnetite provides colour to paints, coatings, concrete, and construction materials.
Strong tinting power allows relatively small additions of Magnetite to produce dark tones.

High-purity Magnetite serves as a raw material for manufacturing ferric chloride and ferric sulphate.
Water-treatment facilities use chemicals derived from Magnetite for coagulation and contaminant removal.

Finely divided Magnetite can adsorb metals and other contaminants from water.
An external magnetic field can subsequently separate contaminant-loaded Magnetite from the treated liquid.

Catalytic reactions involving hydrogen peroxide can be promoted by the iron sites present in Magnetite.
Advanced oxidation processes use Magnetite to support the degradation of selected organic pollutants.

Chemical-processing applications employ Magnetite as a catalyst, catalyst support, or reactive iron source.
Redox activity arising from mixed iron valences contributes to the catalytic behaviour of Magnetite.

Nanometre-sized Magnetite can be dispersed in carrier liquids to prepare ferrofluids.
Magnetic seals, dampers, sensors, and specialised heat-transfer systems may use ferrofluids containing Magnetite.

Research applications use Magnetite nanoparticles in magnetic separation, imaging, sensing, and targeted-delivery systems.
Surface coatings help stabilise Magnetite nanoparticles and control their interaction with surrounding materials.

Exposure to oxygen can gradually oxidise Magnetite into maghemite or hematite.
Temperature, particle size, and atmospheric conditions influence the oxidation rate of Magnetite.

Reduction of Magnetite with carbon monoxide, hydrogen, or carbon-containing materials can produce metallic iron.
This reducibility allows Magnetite to function as an important feedstock in ironmaking processes.

Coprecipitation of Fe²⁺ and Fe³⁺ salts provides a common route for producing synthetic Magnetite.
Careful control of pH, temperature, and oxygen exposure determines the particle size and purity of synthetic Magnetite.

Uses of Magnetite:
Magnetite is a major iron ore mineral (Fe 72.4%, O 27.6% theoretical) processed in blast furnaces and direct reduction plants to produce pig iron, sponge iron (DRI), and ultimately steel; together with hematite it forms the principal feedstock of the global steel industry; magnetite ore beneficiation relies on magnetic separation exploiting the mineral's ferrimagnetism to produce high-grade iron ore concentrate (magnetite concentrates typically 65–70% Fe).
Magnetite-derived iron catalyst (promoted with Al₂O₃, K₂O, and CaO as promoters) is the active phase in the Haber–Bosch process for industrial ammonia synthesis (N₂ + 3H₂ → 2NH₃); the catalyst is prepared by oxidising finely ground iron to magnetite or wüstite, followed by partial reduction to produce a porous Fe/FeO/Fe₃O₄ core-shell structure with high surface area.
Magnetite (specific gravity 5.17–5.18) is used as a dense-medium suspension in coal preparation plants, where ground magnetite suspended in water creates a medium of intermediate density (~1.5–2.0 g/cm³) that allows coal (SG ~1.3–1.4) to float and reject shale (SG ~2.2–2.4) to sink; the magnetite is recovered and recycled magnetically after separation.
Magnetite micro- and nanoparticles are used in high-gradient magnetic separation (HGMS) water treatment — nanoparticles introduced into contaminated water bind to suspended solids, bacteria, heavy metals, and radionuclides and are then magnetically separated and recycled; magnetite nanoparticles are also used as reactive surfaces for groundwater remediation, including arsenic and chromate removal.
Magnetite nanoparticles in ferrofluid formulations are used for targeted drug delivery (magnetic dragging to tumour sites), as MRI T₂ contrast agents (superparamagnetic iron oxide nanoparticles, SPION), and in magnetic hyperthermia cancer therapy; the high specific surface area and biocompatibility of synthetic magnetite nanoparticles are key properties for these biomedical applications.
Magnetite has been the principal ore mineral for rhenium-free iron-based catalysts since the early 20th century, and also serves as a pigment (iron black, Fe₃O₄), polishing compound (jeweller's rouge type), and magnetic recording material; it was the first magnetic recording medium used in German Magnetophon tape recorders (BASF, 1930s) before being superseded by γ-Fe₂O₃.
Magnetite grains in igneous, metamorphic, and sedimentary rocks record the orientation and intensity of the Earth's magnetic field at the time of rock formation (paleomagnetism), providing a critical archive for plate tectonic reconstruction, geomagnetic reversal chronology, and magnetostratigraphy; the Re–Os and U-Pb isotope systems in magnetite-associated minerals provide geochronological constraints.
Biomineralised magnetite — in magnetosome chains of magnetotactic bacteria, in the upper beak of birds for magnetoreception, and in the radula teeth of chitons — represents one of the most biologically active minerals, with ongoing research into its role in human brain tissue (hippocampus, frontal and temporal lobes) and its potential links to neurodegenerative disease via oxidative stress.

Benefits and Advantages of Magnetite:
Magnetite's ferrimagnetism and high specific gravity (5.17–5.18) make it uniquely suited for dense-medium separation and magnetic beneficiation; unlike most industrial minerals, spent magnetite medium can be fully recovered by low-intensity magnetic drum separators and reused indefinitely, making the process both economical and circular.
The Verwey transition of magnetite (abrupt metal-to-insulator electronic phase transition at ~120 K from monoclinic to cubic structure) is one of the most studied and best-characterised solid-state transitions in materials science, making magnetite a reference material for electronic, magnetic, and phase-transition research.
Magnetite's mixed Fe²⁺/Fe³⁺ valence chemistry enables it to participate in both reductive and oxidative reactions, making it an effective reactive mineral surface for environmental remediation (reducing Cr⁶⁺ to Cr³⁺, reductive dechlorination, arsenic co-precipitation) without requiring complex chemical additions.
Magnetite occurs worldwide in economically viable concentrations across multiple deposit types (BIF, skarn, porphyry, placer, and volcanic-associated), providing geographic supply diversity and metallurgical flexibility in beneficiation, making it one of the most geopolitically accessible major metal ores.

Features of Magnetite:
Magnetite occurs most commonly as octahedral crystals bounded by {111} planes and as rhombic dodecahedra, sometimes with striations on dodecahedral faces parallel to the intersection with octahedral faces; twinning on {111} (spinel law, contact twins) is common; it also occurs as granular masses, lamellar, and as fine disseminated grains in rocks; crystal size ranges from submicron (biogenic and detrital) to 10 mm (hydrothermal).
Colour is black to iron-black, occasionally brownish-black in reflected light; luster is metallic to submetallic; streak is black; diaphaneity is opaque; cleavage is indistinct, with very good parting on {111}; fracture is uneven; tenacity is brittle; density 5.17–5.18 g/cm³; refractive index 2.42 (opaque, measured by reflectance); Curie temperature 580°C; Verwey transition ~120 K.
Magnetite's diagnostic characteristics are: (1) strong ferrimagnetism — attraction to a hand magnet and, for lodestone, self-magnetisation; (2) black streak on unglazed porcelain; (3) high specific gravity; (4) black metallic octahedral crystals; these properties together distinguish it from graphite (not magnetic), ilmenite (weakly magnetic, brown streak), hematite (red-brown streak, non-magnetic), and franklinite (weaker magnetism, brown streak).
Magnetite forms solid solutions with ulvospinel (Fe₂TiO₄) — the titanomagnetite series important in igneous petrology and paleomagnetism — and with magnesioferrite (MgFe₂O₄) and jacobsite (MnFe₂O₄); these solid solutions control oxygen fugacity through the QFM (quartz-fayalite-magnetite), HM (hematite-magnetite), and MW (magnetite-wüstite) buffers widely used in experimental petrology.

Mineralogical and Chemical Properties of Magnetite:
Magnetite has IUPAC name iron(II,III) oxide, chemical formula Fe₃O₄ (or Fe²⁺Fe³⁺₂O₄), molar mass 231.53 g/mol, theoretical composition Fe 72.4%, O 27.6%; it belongs to the oxide mineral class, spinel group (inverse spinel structure, space group Fd3m); PubChem CID 16211978; CAS 1317-61-9 (natural magnetite), 1309-38-2 (synthetic Fe₃O₄); InChI=1S/Fe2O3.FeO/c1-4(2)3;1-2, InChIKey SZVJSHCCFOBDDC-UHFFFAOYSA-N.
The inverse spinel structure of magnetite has 32 O²⁻ ions per unit cell (FCC arrangement) with Fe²⁺ occupying all octahedral B-sites (½) and Fe³⁺ split between the tetrahedral A-sites (½) and the remaining octahedral B-sites (½); the electron hopping between Fe²⁺ and Fe³⁺ at octahedral B-sites at room temperature is responsible for the high electrical conductivity (semi-metallic behaviour above the Verwey transition) and ferrimagnetism (net magnetic moment ~4.1 μB per formula unit); below ~120 K (Verwey transition), electron ordering produces a monoclinic distortion and the material becomes an insulator.
Magnetite dissolves slowly in hydrochloric acid; it oxidises in air at ambient temperatures to maghemite (γ-Fe₂O₃) especially at the nanoscale; at high temperatures in air, it converts to hematite (α-Fe₂O₃); it reacts with H₂ and CO at temperatures above ~200°C for industrial reduction to iron (DRI process); it is stable in reducing environments (below the QFM buffer) and can participate in the serpentinisation of peridotite by the reaction: 6(Mg,Fe)₂SiO₄ + 7H₂O → 3(Mg,Fe)₃Si₂O₅(OH)₄ + Fe₃O₄ + H₂.
Magnetite nanoscale behaviour differs significantly from bulk: particles below ~80 nm are single-domain (no magnetic domain walls), particles below ~25 nm are superparamagnetic (no stable remanent magnetisation at room temperature, high susceptibility, useful for SPION biomedical applications), and the Verwey transition temperature and character are strongly grain-size dependent.

Occurrence and Production of Magnetite:
Magnetite occurs in all major geological environments: igneous (crystallises from mafic and ultramafic magmas, abundant in gabbros, basalts, andesites, and ultramafic cumulates), metamorphic (forms during high-grade metamorphism of iron-rich sediments; common in amphibolites and granulites), sedimentary (banded iron formations, beach and river placer deposits, lake and marine sediments), and hydrothermal (skarn deposits, porphyry Cu-Mo systems, iron-oxide-copper-gold — IOCG deposits).
Major magnetite ore districts include: Kiruna iron ore district (Sweden; IOCG-type, world-class); Chilean Iron Belt (Atacama region, Chile); Adirondack Mountains (New York, USA); Tallawang (New South Wales, Australia); Valentines (Uruguay); magnetite BIF deposits (Pilbara, Western Australia; Carajás, Brazil; Iron Range, Minnesota); beach and dune magnetite sands (New Zealand North Island; California; Peru dune field, 250 km², 10% magnetite; Hong Kong); Kediet ej Jill (Mauritania, entirely magnetite); European occurrences in León (Spain), Norway, Romania, and Ukraine.
Magnetite is processed by low-intensity magnetic separation (LIMS) for coarse-grained deposits and high-intensity/high-gradient magnetic separation (HIMS/HGMS) for fine-grained deposits; beneficiated magnetite concentrate (65–70% Fe) is pelletised for blast furnace feed or processed by direct reduction (DR) for DRI/sponge iron; synthetic magnetite is produced by co-precipitation of Fe²⁺/Fe³⁺ solutions with NaOH or NH₃, by thermal decomposition of iron salts, or by hydrothermal synthesis.

Magnetite Material Safety Data Sheet (MSDS):

Handling of Magnetite:
Natural magnetite ore and iron oxide (Fe₃O₄) dust require standard mineral dust handling precautions; inhalation of fine iron oxide dust should be avoided; the ACGIH TLV for iron oxide (as Fe) is 5 mg/m³ (TWA, respirable fraction) and OSHA PEL is 10 mg/m³ as nuisance dust.
Magnetite nanoparticles and fine powder (< 10 µm) require additional precautions due to the potential for deep lung deposition and, for airborne combustion-derived magnetite nanoparticles, potential neurotoxic effects via olfactory nerve transport; use enclosed systems or exhaust ventilation and appropriate respiratory protection for nanomaterial handling.

Magnetite SDS:

Stability and Reactivity of Magnetite:

Chemical stability:
Magnetite is chemically stable under ambient conditions in bulk form.
Magnetite oxidises slowly in air at ambient temperature to maghemite (γ-Fe₂O₃); this process is accelerated at the nanoscale. At elevated temperatures (>400°C in air), conversion to hematite (α-Fe₂O₃) occurs.

Reactivity:
Magnetite dissolves slowly in hydrochloric acid; it is reduced by H₂ and CO at elevated temperatures.
Magnetite participates in the serpentinisation reaction with olivine and water, producing hydrogen gas.

Conditions to avoid:
Fine dust generation (respiratory hazard; iron oxide dust TLV 5 mg/m³).
Exposure to concentrated acids (dissolution with Fe²⁺/Fe³⁺ release).
High temperatures in air (conversion to hematite, releasing lattice oxygen).

Incompatible materials:
Concentrated mineral acids (HCl, H₂SO₄, HNO₃).
Strong reducing agents at elevated temperatures (H₂, CO, C).
Strong oxidising agents (conversion to hematite/Fe²O₃).

Hazardous decomposition products:
Iron oxide fume (Fe₂O₃) upon prolonged high-temperature heating in air — siderosis risk with chronic inhalation.
No toxic gases under normal ambient conditions.

Handling and Storage of Magnetite:

Handling:
Minimise dust generation; use wet methods or local exhaust ventilation in crushing and grinding operations.
Wear appropriate respiratory protection where dust exceeds OEL (ACGIH TLV: 5 mg/m³ TWA as Fe, respirable).
Wash hands after handling; do not eat, drink, or smoke in dusty work areas.
For magnetite nanoparticles: handle in enclosed systems or under local exhaust; use P100 respirator and appropriate skin protection.

Storage:
Store in dry, closed containers; no special temperature requirements for bulk mineral.
Keep magnetite powder away from moisture to prevent surface oxidation and agglomeration.
No flammability, reactivity, or transport hazard for bulk natural mineral.

First Aid Measures for Magnetite:

Inhalation:
Move the affected person to fresh air; if respiratory irritation persists, consult a physician.
For chronic occupational exposure to iron oxide dust, periodic chest X-ray or CT scan monitoring for siderosis (pulmonary iron deposition) is recommended.

Skin contact:
Wash with water; iron oxide is not a primary skin irritant or sensitiser.

Eye contact:
Rinse with water for several minutes; consult a physician if irritation persists.

Ingestion:
Rinse the mouth with water; magnetite is of very low acute oral toxicity; consult a physician if large quantities are ingested.

Firefighting Measures for Magnetite:

Suitable extinguishing media:
Magnetite is non-combustible; use extinguishing media appropriate to surrounding fire.

Specific hazards:
At very high temperatures, magnetite may release iron oxide fumes; siderosis risk for firefighters exposed to iron oxide-containing smoke.

Protective equipment for firefighters:
SCBA and full protective clothing where iron oxide fume may be present.

Accidental Release Measures for Magnetite:

Personal precautions:
Prevent fine dust generation; wear respiratory protection if fine powder is released.

Environmental precautions:
Magnetite is an iron mineral and is not classified as an environmental hazard at bulk scale; prevent large quantities of fine magnetite slurry from entering water courses to avoid elevated iron levels.

Clean-up methods:
Collect mechanically or wet-sweep; magnetite can also be collected using a magnet for spills of magnetic powder; dispose in accordance with applicable regulations.

Exposure Controls / Personal Protective Equipment for Magnetite:

Engineering controls:
Local exhaust ventilation in crushing, grinding, and processing areas; wet methods preferred for dust control.

Eye protection:
Safety glasses or goggles during handling of crushed mineral or oxide powder.

Hand protection:
General purpose gloves for protection from abrasive mineral dust.

Respiratory protection:
P95 (US) or P2 (EU EN 143) particle filter for dusty mineral operations; P100 for iron oxide fume or nanoparticle operations.

Hygiene measures:
Wash hands before breaks and at end of workday; do not eat, drink, or smoke in work areas.

Magnetite Identifiers:
IMA Symbol: Mag
Strunz Classification: 4.BB.05
Dana Classification: 7.2.2.3
CAS Number (natural): 1317-61-9
CAS Number (synthetic Fe₃O₄): 1309-38-2
Chemical Formula: Fe₃O₄ (Fe²⁺Fe³⁺₂O₄)
IUPAC Name: Iron(II,III) oxide
Molecular Weight: 231.53 g/mol
Theoretical Composition: Fe 72.4%, O 27.6%
PubChem CID: 16211978
InChI: InChI=1S/Fe2O3.FeO/c1-4(2)3;1-2
InChIKey: SZVJSHCCFOBDDC-UHFFFAOYSA-N
Crystal System: Isometric (cubic)
Crystal Class: Hexoctahedral (m3m); H-M symbol (4/m 3 2/m)
Space Group: Fd3m (no. 227)
Unit Cell: a = 8.397 Å; Z = 8
Colour: Black; iron-black; brownish-black
Crystal Habit: Octahedral {111}; rhombic dodecahedral; granular massive
Twinning: {111} spinel law (contact twins)
Cleavage: Indistinct; parting {111} very good
Fracture: Uneven
Tenacity: Brittle
Mohs Hardness: 5.5–6.5
Luster: Metallic to submetallic
Streak: Black
Diaphaneity: Opaque
Specific Gravity: 5.17–5.18
Refractive Index: 2.42 (reflectance-based)
Magnetism: Ferrimagnetic; Curie temperature 580°C
Verwey Transition: ~120 K (monoclinic ↔ cubic)
Solubility: Dissolves slowly in HCl
Mineral Group: Spinel group (inverse spinel)
GHS Classification: Not classified as hazardous (bulk natural mineral); iron oxide dust OEL: 5 mg/m³ TWA (ACGIH TLV)
Associated Minerals: Chromite, ilmenite, ulvospinel, pyrrhotite, pyrite, chalcopyrite, hematite, quartz (igneous/metamorphic/hydrothermal)
Major Deposit Types: BIF; skarn; porphyry; placer; IOCG; volcanic-associated

Properties of Magnetite:
Mineral class: Oxide (spinel group)
Chemical formula: Fe₃O₄
Molecular weight: 231.53 g/mol
Theoretical composition: Fe 72.4%, O 27.6%
Crystal system: Isometric (cubic)
Colour: Black; iron-black; brownish-black
Crystal habit: Octahedral; dodecahedral; granular massive
Cleavage: Indistinct; parting {111}
Tenacity: Brittle
Mohs hardness: 5.5–6.5
Luster: Metallic to submetallic
Streak: Black
Transparency: Opaque
Specific gravity: 5.17–5.18
Magnetism: Ferrimagnetic; Curie temp. 580°C
Verwey transition: ~120 K
Melting point: ~1583–1597°C (decomposes)
GHS Classification: Not classified (bulk mineral)
Storage: Dry, closed containers

Magnetite Properties — Specifications:
Product name: Magnetite (Fe₃O₄)
IMA Symbol: Mag
Chemical Formula: Fe₃O₄
IUPAC Name: Iron(II,III) oxide
Molecular Weight: 231.53 g/mol
Theoretical Fe content: 72.4%
Specific gravity: 5.17–5.18
Mohs hardness: 5.5–6.5
Crystal system: Isometric (cubic)
Available grades: Natural ore mineral (run-of-mine); magnetic separation concentrate (65–70% Fe); technical grade iron oxide powder (various particle sizes); synthetic SPION nanoparticles (biomedical)
Storage: Dry, closed containers; away from concentrated acids and moisture
Format: Lump ore; concentrate; powder; nanoparticles (synthetic)
Documents: Product data sheet and CoA available on request

Names of Magnetite:
Magnetite
Iron(II,III) oxide
Ferrous ferric oxide
Ferrosoferric oxide
Magnetic iron ore
Black iron oxide
Iron black
Lodestone (naturally magnetised)
Fe₃O₄
IMA symbol Mag
Strunz 4.BB.05
CAS 1317-61-9
CAS 1309-38-2 (synthetic)
PubChem CID 16211978