Several minerals react when placed within a magnetic field. Some minerals are strongly attracted to the magnet, others are weakly attracted, and one mineral is repelled. There are also several minerals that are attracted to magnetic fields only when heated.
A magnetic field is an area encompassing a magnet or electrical current that has the ability to attract or repel certain objects placed in the field. The closer the object is to the magnet or electrical current, the more powerful the magnetic effect. The presence of iron in a mineral is responsible for the magnetic properties of minerals in virtually all cases.

Magnetic properties of minerals are defined as follows:

• Ferromagnetism, or strong attraction to magnetic fields is exhibited in only few minerals, notably magnetite and pyrrhotite.

• Paramagnetism is weak attraction to magnetic fields. The attraction is usually discernible, but it may be so weak that it is undetectable. Most paramagnetic minerals become strongly magnetic when heated. A small number of paramagnetic minerals, such as platinum, are not essentially paramagnetic, but contain iron impurities which are responsible for the paramagnetism. However, some specimens lacking iron also exist, and these are not paramagnetic. Some examples of paramagnetic minerals are hematite and franklinite.

• Diamagnetism. Only one mineral, bismuth, is diamagnetic, meaning it is repelled from magnetic fields.

• Another property, which is unnamed, is attraction to magnetic fields when heated. Some iron sulfides and oxides become ferromagnetic after heating, as a result of combined sulfur or oxygen ions freeing themselves from the iron. Some minerals may even act as magnets when heated.

• Magnetism. Only a variety of one mineral acts as a magnet, generating magnetic fields. This is the lodestone variety of magnetite, found in only a few deposits throughout the world. Although it is only weakly magnetic, its magnetism is definitely discernible.
  

Lodestone: The magnetism of this magnetic variety of magnetite is clearly visible

Magnetic properties are useful for identifying a mineral, for if observed it can pinpoint a mineral. The most effective testing results are obtained with the use of a powerful magnet. The only minerals that possibly respond to magnets without heating are opaque, metallic-looking minerals.

NOTE: Most mineral guides list minerals attracted to magnetic fields as "magnetic". This may lead to confusion, for there is a difference between "magnetic" (acts as a magnetic field) and "attracted to magnetic fields" (drawn toward magnetic fields). To avoid this confusion, this guide clearly discerns between "magnetic" and "attracted to magnetic fields".

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