Properties - Magnetic
Magnetic susceptibility for a suite of samples from a study area near Silverton Colorado.
Data from McCafferty, A.E., Horton, R.J., Stanton, M.R., McDougal, R.R., and Fey, D.L., 2011, Geophysical, geochemical, mineralogical, and environmental data for rock samples collected in a mineralized volcanic environment, upper Animas River watershed, Colorado: U.S. Geological Survey Data Series 595, 13 p.
PetLab is equipped to make magnetic susceptibility and remanent magnetism measurements.
Magnetic susceptibility is a measure of a materials ability to be magnetized by an external field. For rocks and sediments, the observed magnetic susceptibility is proportional to the sample's magnetic mineral content. Magnetite, maghemite, pyrrhotite and ilmenite are the common magnetic minerals. Magnetic susceptibility measurements are made using a number of different laboratory and field meters. These meters operate at a frequency of about 1,000 Hz and measure "apparent" magnetic susceptibility. Apparent susceptibility measurements can be converted to true susceptibility by accounting for sample shape, mass and volume. At higher frequencies, 30kHz to 3GHz, magnetic properties are determined from S-parameter measurements as described in the high-frequency electrical properties section.
Remanent magnetization is a sample's permanent magnetization in the absence of an external field, and provides a physical record of the Earth's magnetic field history. Remanent magnetism measurements are made with a Schonstedt magnetometer. Rock specimens, up to 2.5 inches across, are measured in a magnetically shielded chamber that contains a fluxgate magnetometer sensor. The sample is rotated to find the maximum signal output which indicates the direction and magnitude of its remanent magnetization.