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Magnetite
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Magnetite is an ancient term, possibly an allusion to the locality, Magnesia, Greece, an early locality for Lodestone.

Discovered in 1845;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Fe³⁺₂Fe²⁺O₄

Iron Oxide

Molecular Weight:

231.54 gm

Composition: 

Classification

Mineral Classification:

Oxides

Strunz 8th Ed. ID:

4/B.02-20

Nickel-Strunz 10th Ed. ID:

4.BB.05

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
B : Metal: Oxygen = 3:4 and similar
B : With only medium-sized cations

Related to:

Spinel Group. Iron Subgroup. Jacobsite-Magnetite Series. Magnesioferrite-Magnetite Series.

Varieties:

Aluminous Magnetite, Hydromagnetite, Ishkulite, Lodestone, Manganmagnetite, Mg-Titanomagnetite, Mushketovite, Nickeloan Magnetite, Silfbergite (of Niggli), Titaniferous Magnetite, Vanado-Magnetite

Synonyms:

Aimantine, Diamagnetite, Ferroferrite, Heraclian, Lodestone, Magnet, Magnetic Iron Ore, Morpholite, Octahedral Iron Ore, Oxydulated Iron, Sideritis, Syderite

Crystal Data

Crystallography:

Isometric - Hexoctahedral

Crystal Habit:

Typically octahedral, less commonly dodecahedral, striated on {011}, to 25 cm, very rarely cubic; skeletal, granular, massive.

Twinning:

On {111} as both twin and composition plane, the spinel law, as contact twins, flattened, lamellar.

Physical Properties

Cleavage:

Parting on {111} very good; also reported as parting planes: {001}, {011}, {138}.

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.5

Density:

5.175 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Strongly magnetic

Optical Properties

Color:

Black, Gray with Browninsh tint in reflected light

Transparency:

Opaque, Translucent on very thin edges

Luster:

Metallic to SubMetallic, may be Dull

Refractive Index:

2.42  (Isotropic)

Birefringence:

0.00  (Isotropic)

Dispersion:

Strong; r > v

Occurances

Geological Setting:

A common accessory mineral in igneous and metamorphic rocks, in which magmatic segregation or contact metamorphism may produce economic deposits. Extensive deposits in sedimentary banded iron formations; a biogenic product; important detrital deposits.

Common Associations:

Chromite, Ilmenite, Ulvospinel, Rutile, Apatite, Silicates (igneous); Pyrrhotite, Pyrite, Chalcopyrite, Pentlandite, Sphalerite, Hematite, Silicates (hydrothermal, metamorphic); Hematite, Quartz (sedimentary).

Common Impurities:

Mg, Zn, Mn, Ni, Cr, Ti, V, Al

Type Locality:

Magnesia, Greece

Year Discovered:

1845

View mineral photos:

Magnetite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Magnetite is a naturally magnetic mineral that is a member of the Iron Subgroup of the Spinel Group of minerals that also includes Franklinite. The magnetism of Magnetite is due to two different types of Iron; Fe +2 and Fe +3. The arrangement of these two types of Iron causes a transfer of electrons between the two which generates the magnetic field.

There are many localities for Magnetite, even for fine crystals. In Sweden, at Falun, Kiruna, Vastanfors, and elsewhere. At Arendal, Norway. From Zlatoust and Magnetigorsk, Ural Mountains, Russia. In the Zillertal, Tirol, Austria. From Traversella, Piedmont, Italy. In Switzerland, at Binntal and Rimpfischwang, Valais, and elsewhere. In the Gardiner complex, beyond the head of Kangerdlugssuaq Fjord, Greenland. From Bancroft, Ontario, Canada. In the USA, around Lake Sanford, Essex County, and in the Tilly Foster mine, Brewster, Putnam County, New York; at Magnet Cove, Hot Springs County, Arkansas; in the Iron Springs district, Iron County, Utah. From the Cerro del Mercado, Durango, Mexico. At Itabira, Minas Gerais, Brazil.
 

  
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