A geophysical prospecting method that maps variations in the magnetic
field of the Earth that are attributable to changes of structure or
magnetic susceptibility in certain near-surface rocks. Sedimentary rocks
generally have a very small susceptibility compared with igneous or
metamorphic rocks, and most magnetic surveys are designed to map structure
on or within the basement, or to detect magnetic minerals directly. Most
magnetic prospecting is now carried on with airborne instruments.
Dictionary of Mining, Mineral, and Related Terms