Is Limestone Magnetic ? 5 Facts You Should Know !

Limestone is a sedimentary rock composed of calcium carbonate as the main compound. Now, let us discuss the magnetic nature of limestone.

A pure form of limestone (CaCO₃) is non-magnetic because it does not contain any magnetic compound in its composition, but at high temperatures, all limestone can be magnetic. Limestone consists of sand-sized grains in the carbonate matrix that plays a vital role in the magnetic behavior of limestone.

Limestone has variability in the mineral composition, which leads to variability in magnetic properties also. In this post, let us find the reason for limestone’s magnetic nature and learn some interesting facts related to limestone magnetism.

Why is limestone magnetic?

If a material shows any response to the magnetic field, then the material is considered magnetic. Let us reason out the magnetic behavior exhibited by the limestone.

Limestone containing is magnetic at high temperatures because, at a high temperature above 500°C, a change in the mineralogy occurs in limestone that leads to the growth of magnetite in the grains. Extremely small grain size and low concentration carry the magnetization, which provides a ferromagnetic phase in limestone.

The newly formed magnetite interprets the thermal demagnetization of compounds in the limestone at high temperatures. Some limestone containing traces of iron can exhibit magnetic behavior as the iron itself is a good magnetic material.

Limestone magnetic properties

Limestone is a white or gray-colored sedimentary rock that can appear blackish if it contains iron or manganese traces. Now, let us list the magnetic properties of limestone.

Limestone exhibits either non-magnetic or ferromagnetic behavior.
The value of the magnetic susceptibility of limestone is positive.
Limestone can easily undergo thermal demagnetization at high temperatures.
The susceptibility and coercivity of limestone frequently change at a lower temperature.

Limestone magnetic susceptibility

Magnetic susceptibility in mineralogy monitors the discrete samples during thermal demagnetization. Let us know the magnetic susceptibility possessed by limestone.

The magnetic susceptibility of the limestone varies from 0 to 3×10^-3 SI units. The value of susceptibility shows the dualism in the magnetic behavior of the limestone. The limestone having susceptibility 0 indicates the non-magnetism of limestone, and positive values indicate the limestone’s magnetism.

The susceptibility variation is due to the occurrence of thermal demagnetization in limestone. The metastable minerals such as maghemite, goethite, or pyrrhotite present in limestone break down at low temperatures causing variation in the magnetic susceptibility of limestone.

Limestone magnetic separation

Magnetic separation enhances the effective separation of contaminants present in the mineral ore. Let us focus on the process of magnetic separation involved in limestone.

The magnetic separation method does the separation of limestone and other magnetic minerals. The separator consists of two drums with magnets where the finely powdered ore is made to move. Magnetic particles drift by the drum and collect in one container. Limestone being non-magnetic collected in another container.

The magnetic separation method easily separates the iron traces in the limestone ore as the magnet strongly attracts iron. The paramagnetic minerals also can be separated from this method. The magnetic separation method also separates the limestone in the bauxite ore.

How is limestone deposited?

Limestone is rich in fossil minerals whose formation is associated with the living organism. Let us study about deposition and formation of limestone.

Limestone is usually deposited in marine or freshwater resources through biological or non-biological means. The dissolved calcium in the water precipitates to form limestone, deposited under the shallow sea or lake bed, and then can be extracted.

The biological means of deposition of limestone is done by decomposing an animal shell containing calcium. The non-biological deposition is done directly from the chemical sedimentary rocks, but their abundance is less than biological deposition.

Conclusion

Let us conclude this post by stating that limestone is non-magnetic in its purest form and normal temperature, but they exhibit magnetism at high temperature. The presence of magnetite or iron makes the limestone magnetic. The susceptibility value of limestone gives evidence of duality in exhibiting the magnetism of limestone.