Magnetite and ferromagnetic minerals have magnetic susceptibility. Other ferromagnetic minerals are scarce in number and occur seldom. Pyrhotite, ilmenite, specularite, franklinite, and cubanite are the most significant. Magnetite is a black powder that is found in abundance in various rocks including magnetite schist, granitic pegmatites, gneissic rocks, etc.
Some rocks such as granite, gneiss, and sandstone contain little or no iron but do have silica and alkalis which cause them to be magnetic. These rocks are usually found near iron ore deposits. When exposed to air, the silicon and oxygen in these rocks combine to form silica, which is non-magnetic, so the presence of iron inside the rock prevents it from being attracted to either the Earth's or the Moon's magnetic field.
Some rocks such as hematite, goethite, and lepidocrocite are not magnetic but can become so when they are oxidized. This happens when these rocks are found in areas with high levels of air pollution. Oxidation removes the iron from these rocks causing them to lose their magnetic property.
Rocks consist mainly of silicon dioxide (SiO2) and iron oxide (Fe2O3).
Some of the most prevalent minerals with magnetic characteristics are as follows:
Magnetite is a widely used magnetic mineral. It is the main ingredient in many magnets.
Other magnetic minerals include: maghemite γ-Fe(OH)3, hematite α-FeO(OH), and ferrihydrite (δ-FeOOH). These minerals are all found in nature and are used as additives in some crafts and toys. They are not used in any practical applications for magnets due to their low density (magnetite has a density of about 3585 kg/m3).
The majority of magnets today are made from synthetic materials, such as cobalt-containing compounds.
There are several types of magnets: neodymium-, samarium-, and lodestone-based magnets.
Neodymium magnets are made by combining iron with nitrogen and other elements. This creates a compound called iron nitride that is very attractive (like gold is to most miners) because it is strong and does not decay over time like other metals would.
Samarium magnets are made by combining iron with samarium and other elements.
Magnetite, a very common black metallic mineral, is also one of the most significant iron ores in contemporary society, occurring in a range of igneous rocks, pegmatites, contact metamorphic rocks, and hydrothermal veins. Magnetite seldom develops in sedimentary conditions on our current Earth. However, it is found in some rare cases where other elements are present that cause magnetic minerals to form more readily.
Although not a metal in itself, magnetite has been used as a pigment in art and jewelry, and as an additive to steel to improve its quality as a building material. It is also employed as a filling for tooth cavities to prevent decay due to its ability to attract iron bacteria in the mouth.
The chemical formula for magnetite is Fe3O4. This compound contains iron, oxygen, and magnesium (as well as smaller amounts of other elements). Although iron is essential to life, pure magnetite is not biocompatible- it will dissolve in water to release free iron ions that can be toxic if consumed by animals or humans. However, magnetite occurs in nature along with other substances that contain iron but no oxygen, such as greigite and hematite. These minerals protect themselves by forming a surface coating of organic molecules called ligands. The type of ligand determines what types of cells can consume it.
Magnetite is a simple mineral to identify. It is one of just a few minerals that is attracted to a standard magnet. It is a black, opaque, submetallic to metallic mineral with a Mohs hardness ranging from 5 to 6.5. It is frequently found in isometric crystals. It is nature's most powerfully magnetic material. Magnetite is used in medical imaging techniques including MRI and X-ray computed tomography.
Other magnetic minerals include: maghemite (γ-Fe³O_Ν), ferrihydrite (α-FeOOH), hematite (α-Fe²O_3), goethite (α-FeOOH), limonite Mn(OH)_2•xH_2O, lepidocrocite (γ-MnO_2). Some non-mineral substances are also weakly magnetic. These include synthetic polymers such as nylon and Teflon, and natural products such as spider silk and bone tissue.
Minerals are elements that form solid solutions with other elements under conditions found in the earth's crust. The term "magnetic" describes a substance that contains atoms with unpaired electrons; these atoms can act as magnets. Atoms with paired electrons cannot attract each other but do not resist being pulled by an external source of magnetism. Minerals are generally composed of many different types of atoms bonded together into large structures. They often have very interesting physical properties which may be useful in materials science applications.
Magnetite gets its name from the fact that it is a natural magnet. This is a distinctive feature of the mineral. Magnetite is a frequent accessory mineral in igneous rocks as well as a detrital mineral, notably on the beaches west of Auckland (black sand).
Furthermore, magnetite is used as a pigment in both oil and water-based paints.
Finally, some varieties of iron ore contain large amounts of magnetite. One common variety is limonite. This is used to make magnetic needles and paint.
Limonite contains up to 90% magnetite. The other 10% is made up of impurities such as silica, aluminum, calcium, and potassium.
Magnetite is a hard, black mineral with a metallic luster that is rare in nature. It is composed of ferric oxide (Fe3O4) molecules clustered together. The crystal structure of magnetite means that it is susceptible to demagnetization; that is, even if it is exposed to a strong magnetic field, it will not retain its magnetism.
This susceptibility to demagnetization makes magnetite useful for storing data in devices such as hard drives. The information can be encoded on the disk, placed near or even inside a piece of metal with an intense magnetic field applied, and later retrieved when required.
Magnetic characteristics Magnetite's interactions with other iron-rich oxide minerals, such as ilmenite, hematite, and ulvospinel, have been extensively researched; the reactions between these minerals and oxygen determine how and when magnetite keeps a record of the Earth's magnetic field. When temperatures are low, the magnetite records the last strong magnetic field that it experienced (before becoming frozen in ice). As temperatures rise, the magnetite loses this memory of its original orientation, because the magnetic moment it contains is not stable at those temperatures.
As early as 1820, Abraham Gottlob Werner described magnetite as being "magnetically susceptible." In 1879, Carl Vogel found that magnetite retains its magnetic properties after it has been heated to 1000°C (1832°F) or cooled from 1500°C (2732°F). He also discovered that it loses its magnetism if exposed to air for more than six months.
Since then, researchers have tried to explain why some rocks contain large amounts of magnetite while others do not. They have also searched for ways to use the magnetite found in rocks to learn more about their history. It is estimated that up to 9% of the Earth's crust may be made up of magnetite.
The origin of magnetite is still not well understood. Some scientists believe that it is formed in the Earth's mantle and rises to the surface with volcanic lava.