Magnetic mineralogy is the study of the magnetic

Magnetism

Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...

 properties of minerals. The contribution of a mineral to the total magnetism of a rock depends strongly on the type of magnetic order or disorder. Magnetically disordered minerals (diamagnets and paramagnets) contribute a weak magnetism and have no remanence

Remanence

Remanence or remanent magnetization is the magnetization left behind in a ferromagnetic material after an external magnetic field is removed. It is also the measure of that magnetization. Colloquially, when a magnet is "magnetized" it has remanence...

. The more important minerals for rock magnetism

Rock magnetism

Rock magnetism is the study of the magnetic properties of rocks, sediments and soils. The field arose out of the need in paleomagnetism to understand how rocks record the Earth's magnetic field. This remanence is carried by minerals, particularly certain strongly magnetic minerals like magnetite...

 are the minerals that can be magnetically ordered, at least at some temperatures. These are the ferromagnets, ferrimagnets and certain kinds of antiferromagnets. These minerals have a much stronger response to the field and can have a remanence.

Non-iron-bearing minerals

Most minerals with no iron content are diamagnetic. Some such minerals may have a significant positive susceptibility

Magnetic susceptibility

In electromagnetism, the magnetic susceptibility \chi_m is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field...

, for example serpentine, but this is because the minerals have inclusions containing strongly magnetic minerals such as magnetite

Magnetite

Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

. The magnetic susceptibility

Susceptibility

*In physics, the susceptibility of a material or substance describes its response to an applied field. There are many kinds of susceptibilities, for example:These two susceptibilities are particular examples of a linear response function;...

 of such minerals is negative and small (Table 1).

Table 1. Susceptibilities of non-iron-bearing minerals

Mineral	Volume susceptibility Susceptibility *In physics, the susceptibility of a material or substance describes its response to an applied field. There are many kinds of susceptibilities, for example:These two susceptibilities are particular examples of a linear response function;...  at room temperature (SI)
graphite Graphite The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...	-80 to -200
calcite Calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...	-7.5 to -39
anhydrite Anhydrite Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...	-14 to -60
gypsum Gypsum Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...	-13 to -29
ice Ice Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...	-9
orthoclase Orthoclase Orthoclase is an important tectosilicate mineral which forms igneous rock. The name is from the Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Alternate names are alkali feldspar and potassium feldspar...	-13 to -17
magnesite Magnesite Magnesite is magnesium carbonate, MgCO3. Iron substitutes for magnesium with a complete solution series with siderite, FeCO3. Calcium, manganese, cobalt, and nickel may also occur in small amounts...	-15
forsterite Forsterite Forsterite is the magnesium rich end-member of the olivine solid solution series. Forsterite crystallizes in the orthorhombic system with cell parameters a 4.75 Å , b 10.20 Å and c 5.98 Å .Forsterite is associated with igneous and metamorphic rocks and has also been found in meteorites...	-12
halite Halite Halite , commonly known as rock salt, is the mineral form of sodium chloride . Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on the amount and type of impurities...	-10 to -16
galena Galena Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...	-33
quartz Quartz Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...	-13 to -17
celestine Celestine Celestine may refer to:Popes of the Roman Catholic Church:* Pope Celestine I * Pope Celestine II * Pope Celestine III * Pope Celestine IV * Pope Celestine V *Antipope Celestine II Other...	-16 to -18
sphalerite Sphalerite Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...	-31 to -750

Iron-bearing paramagnetic minerals

Most iron-bearing carbonates and silicates are paramagnetic at all temperatures. Some sulfides

Sulfide mineral

The sulfide minerals are a class of minerals containing sulfide as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts...

 are paramagnetic, but some are strongly magnetic (see below). In addition, many of the strongly magnetic minerals discussed below are paramagnetic above a critical temperature (the Curie temperature or Neel temperature

Néel temperature

The Néel temperature or magnetic ordering temperature , TN, is the temperature above which an antiferromagnetic material becomes paramagnetic—that is, the thermal energy becomes large enough to destroy the macroscopic magnetic ordering within the material....

). In Table 2 are given susceptibilities for some iron-bearing minerals. The susceptibilities are positive and an order of magnitude or more larger than diamagnetic susceptibilities.

Table 2. Susceptibilities of some paramagnetic minerals

Mineral	Volume susceptibility Susceptibility *In physics, the susceptibility of a material or substance describes its response to an applied field. There are many kinds of susceptibilities, for example:These two susceptibilities are particular examples of a linear response function;...   (SI)
garnet Garnet The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...	2,700
illite Illite Illite is a non-expanding, clay-sized, micaceous mineral. Illite is a phyllosilicate or layered alumino-silicate. Its structure is constituted by the repetition of tetrahedron – octahedron – tetrahedron layers. The interlayer space is mainly occupied by poorly hydrated potassium cations...	410
montmorillonite Montmorillonite Montmorillonite is a very soft phyllosilicate group of minerals that typically form in microscopic crystals, forming a clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite family, is a 2:1 clay, meaning that it has 2 tetrahedral sheets sandwiching a central...	330-350
biotite Biotite Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula . More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers...	1,500-2,900
siderite Siderite Siderite is a mineral composed of iron carbonate FeCO3. It takes its name from the Greek word σίδηρος sideros, “iron”. It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus...	1,300-11,000
chromite Chromite Chromite is an iron chromium oxide: FeCr2O4. It is an oxide mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite ; substitution of aluminium occurs leading to hercynite .-Occurrence:Chromite is found in...	3,000-120,000
orthopyroxene	1,500-1,800
fayalite Fayalite Fayalite is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system with cell parameters a 4.82 Å, b 10.48 Å and c Å 6.09.Iron rich olivine is a relatively common constituent of acidic and...	5,500
olivine Olivine The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....	1,600
jacobsite Jacobsite Jacobsite is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is MnFe2O4 or with oxidation states and substitutions:2O4....	25,000
franklinite Franklinite Franklinite is a mineral with formula ZnFe2O4. It is associated with the Franklin Mine and Sterling Hill Mines in New Jersey.-See also:* Spinel* Classification of minerals* List of minerals-References:*...	450,000

Iron-titanium oxides

Many of the most important magnetic minerals on Earth are oxides of iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 and titanium

Titanium

Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

. Their compositions are conveniently represented on a ternary diagram with axes corresponding to the proportions of ⁴⁺, ²⁺, and ³⁺. Important regions on the diagram include the titanomagnetites, which form a line of compositions for between 0 and 1. At the end is magnetite

Magnetite

Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

, while the composition is ulvöspinel

Ulvöspinel

Ulvöspinel or ulvite is an iron titanium oxide mineral with formula: Fe2TiO4 or TiFe2+2O4. It forms brown to black metallic isometric crystals with a Mohs hardness of 5.5 to 6...

. The titanomagnetites have an inverse spinel crystal structure and at high temperatures are a solid solution

Solid solution

A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...

 series. Crystals formed from titanomagnetites by cation-deficient oxidation are called titanomaghemites, an important example of which is maghemite

Maghemite

Maghemite is a member of the family of iron oxides. It has the same structure as magnetite, that is, it is spinel ferrite and is also ferrimagnetic.Maghemite can be considered as an Fe-deficient magnetite with formula...

. Another series, the titanohematites, have hematite

Hematite

Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...

 and ilmenite

Ilmenite

Ilmenite is a weakly magnetic titanium-iron oxide mineral which is iron-black or steel-gray. It is a crystalline iron titanium oxide . It crystallizes in the trigonal system, and it has the same crystal structure as corundum and hematite....

 as their end members, and so are also called hemoilmenites. The crystal structure of hematite is trigonal-hexagonal. It has the same composition as maghemite

Maghemite

Maghemite is a member of the family of iron oxides. It has the same structure as magnetite, that is, it is spinel ferrite and is also ferrimagnetic.Maghemite can be considered as an Fe-deficient magnetite with formula...

; to distinguish between them, their chemical formulae are generally given as γ for hematite and α for maghemite.

Iron sulfides

The other important class of strongly magnetic minerals is the iron sulfide

Iron sulfide

Iron sulfide or Iron sulphide refers to a chemical compound of iron and sulfur with a wide range of stoechiometric formulae and different crystalline structures.-Natural minerals:By increasing order of stability:...

s, particularly greigite

Greigite

Greigite is an iron sulfide mineral with formula Fe3S4. It is the sulfur equivalent of the iron oxide magnetite . It was first described in 1964 for an occurrence in San Bernardino County, California, and named after the mineralogist and physical chemist Joseph W...

 and pyrrhotite

Pyrrhotite

Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...

.