GeoClassroom Physical Geology Historical Geology Structure Lab Mineralogy Petrology


Magnetic fields are created by charged particles in motion.

The extent of magnetism that a mineral displays is controlled by the atomic properties of certain elements and the pairing status of electrons.

    If electrons pair, the magnetic fields created by their different spin directions cancel out.

    If an electron is unpaired, it retains a unidirectional field and can be thought of as a tiny magnet with a magnetic moment.

Because unpaired electrons are common in the transition metals, and transition metals are common constituents of minerals, these elements are often responsible for magnetism in minerals.

Some terms & definitions:

  1. Paramagnetism: Paramagnetic minerals become slightly magnetic when an external magnetic field is applied, but lose this magnetism when the field is removed.

    • usually occurs in minerals that initially contain a random distribution of magnetic moments

        In materials with a random distribution of magnetic domains the magnetic moments tend to cancel one another out. However, external forces can cause the domains to align with one another.

        example: olivine

  2. Ferromagnetism: Ferromagnetic minerals become magnetic when an external magnetic field is applied, and can RETAIN this magnetism when the field is removed.

    • magnetic domains with aligned dipoles exist within mineral

      - Curie temperature: can lock in magnetic direction if material is cooled below it
      - can destroy magnetic property if heated above it

        example: metallic iron

  3. Ferrimagnetism: antiparallel magnetic moments that are non-equal, result in a net magnetic moment - permanent magnetic domains

      -600-580oC - lock in magnetism as cooling through curie temp.

        example: magnetite

  4. Diamagnetism: no magnetic behavior at all

      -contain only paired electrons - no unpaired electrons
      -no transition metals present

All Pages Copyright © GeoClassroom. All Rights Reserved.