A rock containing magnetic minerals loses its permanent magnetism when heated up to a critical temperature, referred to as Curie temperature or Curie point, Tc. On the atomic level, below Tc, the magnetic moments are aligned in their respective domains, and even a weak external magnetic field results in a magnetization. As the temperature increases to Tc and above, fluctuations due to the increase in thermal energy destroy that alignment, and the rock becomes paramagnetic.
Magnetic Minerals and Curie Temperature
The most important magnetic rock-forming minerals are oxides of iron and titanium, and their compositions can be represented in the FeO-TiO2-Fe2O3 ternary diagram. Among the three major solid-solution series identified in this system, the titanomagnetite series, Fe3-xTixO4 (with 0 ≤ x ≤ 1), plays a major role in controlling rock magnetism (Stacey 1992). Above 600 °C there is a continuous solid solution in the two-component series magnetite (Fe3O4...
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