The mineral magnetite

Chemical Formula

Fe²⁺Fe³⁺₂O₄

Composition

Iron oxide. May contain many impurities partially replacing both the first and the second iron.

Variable Formula

(Fe,Mn,Mg,Zn,Ni)²⁺ (Fe,Al,Cr,Mn,V)³⁺₂O₄

Color

Black

Streak

Black

Hardness

5½ - 6½

Crystal Forms
and Aggregates

(Isometric) Crystals are usually well-shaped octahedrons, and less commonly dodecahedrons. They may also be an interesting combination of the two. Seldom occurs in cubic crystals. Crystals are usually striated, and some octahedral crystals contain layer growths. Also occurs massive, grainy, in veins, as large embedded grains, and as rounded crystals.

Transparency

Opaque

Specific Gravity

4.9 - 5.2

Luster

Metallic

Cleavage

None. May exhibit parting.

Fracture

Subconchoidal to uneven

Tenacity

Brittle

Other ID Marks

Strongly attracted to magnetic fields ("ferromagnetic")

Varieties

Lodestone - Massive, magnetic variety of magnetite (acts as a magnet)

Titano-magnetite - Titanium-rich variety of magnetite

Chrome-magnetite - Chromium-rich variety of magnetite

In Group

Oxides ; Multiple oxides ; Spinel group

All About

The magnetic variety Lodestone only comes from a few areas. It is the only mineral that acts as a magnet. Although its magnetism is weak, it is strong enough to attract large nails. Due to its magnetic properties, very fine iron filings (usually originating from the mineral itself) cling to its surfaces.

Magnetite may form a yellow-brown rust coating if washed or kept in a moist area. If a specimen must by washed, it should be dried immediately. To prevent rusting, specimens should be stored in dry areas.

Hematite commonly forms pseudomorphs over Magnetite. These pseudomorphs are known as Martite, and their appearance may be similar to regular Magnetite. However, they are only weakly attracted to magnetic fields, and have a reddish-brown streak.

Uses

Magnetite is an important ore of iron. Its perfect crystals are also famous among mineral collectors. This mineral is of scientific interest because of its special magnetic properties.

Striking Features

Strong attraction to magnets, hardness, and streak

Popularity

Prevalence

Demand

Distinguishing
Similar Minerals

Franklinite - only weakly attracted to magnetic fields
Spinel - not attracted to magnetic fields, has a white streak
Ilmenite - lighter streak
Chromite - has a brownish streak

Commonly
Occurs With

Calcite, Phlogopite, Talc, Pyrite, Ilmenite, Hematite, Apatite, Garnet, Chlorite

Noteworthy
Localities

Magnetite is a common mineral, and exists in numerous localities. Only the finest are mentioned.
Some famous worldwide occurrences are Binnental, Switzerland; Pfitschal, Tyrol, Austria; and the Palabora Mine, Transvaal, South Africa. The largest Magnetite deposits are in northern Sweden. Other enormous deposits are in Norway, Romania, and Russia.
In the U.S., the magnetic variety Lodestone comes from the Iron Springs area (Dixie National Forest), Washington and Iron counties, Utah; and Magnet Cove, Hot Spring Co., Arkansas.
Large masses come from Franklin, Sussex Co., New Jersey, and perfect octahedral crystals from Chester, Windsor Co., Vermont. Interesting dodecahedral crystals were at one time abundant at the Tilly Foster Mine, Brewster, Putnam Co., New York. Large cubic crystals occur in Balmat, St. Lawrence Co., New York, and the French Creek Mine, St. Peters, Chester Co., Pennsylvania has produced some large octahedrons.
Large octahedrons were found in Monroe, Orange Co., New York and in Laurel Hill (Snake Hill), Secaucus, Hudson Co., New Jersey. Massive and poorly crystallized examples of this mineral can still be found in abundance in the dumps of the 19th century iron mines in the Ramapo Mountains (Orange and Rockland Counties), New York.

Picture Icon
Links

Picture Links

1. Cluster of rusted Magnetite crystals
2. Elongated octahedral crystal
3. Octahedral crystal
4. Magnetic "Lodestone"
5. Magnetite in Calcite