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 actually 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. In
virtually all cases, the presence
of the element iron as a component of the mineral's chemical structure is responsible
its magnetic properties.
Magnetic properties of minerals are defined as follows:
Ferromagnetism describes strong attraction to
magnetic fields. This property is exhibited in 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 on its own. This mineral is Lodestone,
the magnetic variety of Magnetite, which found in only a few
deposits throughout the world. Although it is only weakly magnetic, its magnetism is
definitely discernible.
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 makes a distinction between "magnetic" and
"attracted to magnetic fields".
