Lodestone: definition and magnetic properties

Magnetite is a piece of magnetite which has become naturally magnetized. The name magnetite comes from the Middle English term “lode” which means path or journey, so the term magnetite is a stone that opens the way.

Lodestone has a unique definition lending in part to the magnetic properties found in this unique stone. The term reflects one of the earliest uses of magnetite as a natural magnetic compass, which was widely used in navigation.

Magnetite is an iron oxide with the chemical formula Fe3O4. Magnetite is black or dark brown in color, and small pieces of magnetite are found in most igneous rocks as well as some sedimentary rocks. Magnetite can be found in many parts of the world, including South America, Australia, the United States, Europe, and China. High concentrations of magnetite, the naturally magnetized version of magnetite, have been found in Tanzania and are known to affect compass readings. The magnet is usually found near the surface of the earth.

As a mineral, magnetite has a crystalline microstructure. This means that the atoms that make up magnetite are structured in a highly ordered fashion within a specific lattice framework. In the case of magnetite, the crystal system is isometric, which means that the unit cell of the crystal is a cube. The most common form in which to find magnetite is in the form of octahedral crystals.

The mineral magnetite is naturally attracted to a magnetic field but is not itself a magnet (i.e. it does not generate a magnetic field).

How does magnetite become magnetic?

To become a magnetite, magnetite must be magnetized. Ordinary magnetite is not magnetic and, in fact, most magnetites cannot be magnetized at all. In order for magnetite to be magnetized, it must have a certain crystal structure and a certain chemical composition. Magnetite is largely formed of magnetite, but it also contains inclusions of maghemite (oxidized magnetite) and other metal ion impurities. These impurities and inclusions make the crystal structure of the magnetite inhomogeneous and allow the mineral to resist demagnetization once it has been magnetized.

It was first hypothesized that the Earth’s magnetic field caused pieces of magnetite to magnetize to form magnetite. However, it has been found that the Earth’s magnetic field is too weak (at 0.25-0.65 Gauss) to cause such a change in the mineral magnetite. Since then, it has been theorized that the magnetite that becomes magnetized to form the magnetites discovered by humans does so by lightning.

Lightning is the result of an electrical imbalance between storm clouds and the ground. The imbalance is unstable and is corrected by the discharge of electricity in the form of electric current. The electric current appears like lightning because the rapid flow of electrons from the cloud to the ground creates a plasma that emits black body radiation in the form of visible light. When lightning strikes the earth, it briefly creates a very strong electromagnetic field. It is this very strong magnetic field that is believed to magnetize magnetite, creating magnetite. Since magnetites are typically found near the earth’s surface, not deeply buried in the ground, it is very possible that lightning is indeed what provides the magnetic field necessary to magnetize magnetite into magnetite.

In the 1500s, Dr. William Gilbert, who was the first scientist in the field of paleomagnetism (the study of the magnetism of rocks), worked to discover the rules governing the magnetism of magnetite and the uses of magnetite, as well as how the properties of magnetite could be studied to better understand the Earth’s magnetic field. Dr Gilbert discovered that magnetization can also occur with the help of heat, in a process called thermoremanent magnetization where an object is heated and then cooled in the presence of a magnetic field.

How does magnetism work?

Magnetism is a force that causes the attraction or repulsion of objects that can be affected by the force field.

Magnetism is caused by the spin of electrons in atoms of a magnetic material. Electrons are negatively charged subatomic particles that have a certain direction relative to their spin. When an electron is unpaired, there is no other electron to spin in the opposite direction and cancel out the small magnetic field generated by the unpaired spinning electron. If all of the unpaired electrons in a material rotate in random directions, then the strength of the magnetic field exerted by the material is weak or completely nonexistent. However, if all the unpaired electrons were spinning in the same direction, the result could be a strong magnetic field generated by the material.

As an example, each iron atom has four unpaired electrons which all have the same spin direction. When an object that generates a relatively strong magnetic field, such as a magnetite, has repeatedly passed through a piece of iron in the same direction, all of the unpaired electrons in each iron atom align and cause the piece to magnetize. of iron. .

What was magnetite used for?

When a piece of magnetite hangs from a string and allows free planar motion, it will align with the north-south polarity of the Earth’s magnetic field along the longest axis of the magnetite. Naturally, this property of magnetite led it to be used as a natural compass. When a piece of iron is touched by a magnetite, the iron will temporarily become magnetized and also align with the Earth’s magnetic field, pointing north and south; this is how the first compass needles were made.

Since 600 BC, people have known about the magnetic properties of magnetite. The ancient Greeks believed that magnetite had a soul, which gave it its “magical” properties. The Chinese used the magnet not only as a compass but also as a tool to predict the future. With the understanding of magnetism we have today, magnetite is more commonly used as a teaching tool to help show students how magnetism works. Through the ages, Lodestone has taken an incredible journey with humanity.


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