Mineral magnetic susceptibility
Magnetic susceptibility is a measure of the response of a material to an externally applied magnetic field and is expressed in terms of the ratio of the magnetization induced in the material to the strength of the applied field. It is a fundamental property of a material that reflects the types and concentrations of the minerals in the material.
The mineral magnetic susceptibility (MMS) measures the response of a mineral to an externally applied magnetic field and is expressed as the ratio of the magnetization induced in the mineral to the strength of the applied field. MMS provides valuable geologic information about the source and depositional environment of the rock. This information can be used to understand the nature of a rock, its age, and its geologic history.
The magnetic susceptibility of a mineral is thought to be related to the type, properties, and concentration of the iron-bearing minerals present, as well as the physical state of the iron-bearing minerals. Magnetic susceptibility is greatly affected by the presence of paramagnetic and iron-bearing minerals like magnetite, hematite, goethite, and pyrite.
The value of the MMS is expressed in terms of volume susceptibility (m3/kg or SI unit) or SI unit (SI=m/kg). The SI unit is most common as it is universally accepted and is used in a variety of geophysical applications and studies. The unit is also used to compare different minerals and rocks.
The most common technique for measuring mineral magnetic susceptibility is the susceptibility bridge, which is composed of solenoids of known permeability with an adjustable “balance” coil. A sample containing iron-bearing minerals is placed between the two coils and a low-level DC current is applied to the balance coil. The strength of the current is adjusted until it is equal to the field strength of the sample. The current is then measured and the magnetic susceptibility of the sample is calculated.
Other techniques used to measure mineral magnetic susceptibility include optical magnetometers and the use of SQUID (superconducting quantum interference device) technology. Optical magnetometers measure the magnetic activity of a sample by passing light through the sample and detecting the Faraday effect. SQUID devices are able to measure extremely small changes in magnetic field.
MMS measurements can be used to identify different minerals in samples, provide evidence of depositional environment, and assess the nature of a rock’s age and geologic history. It can be used for ore and mineral exploration, identifying underground water, mapping sediments, and locating concealed oil and gas deposits.
In summary, mineral magnetic susceptibility is a property of a mineral that reflects the types, properties, and concentrations of the minerals in the material. It is measured using various techniques and provides valuable geologic information about the source and depositional environment of the rock. MMS measurements can be used for ore and mineral exploration, identifying underground water, mapping sediments, and locating concealed oil and gas deposits.
