The resulting configuration shows a narrow intrusive pipe that widens abruptly as it reaches the surface. The structure of the pipe loosely resembles a stemmed wine glass. When electrons spin randomly the net result is that their magnetic fields cancel each other and the substance containing them does not display magnetic properties. However, when magnetic substances are subjected to a strong external magnetic field the electrons tend to spin in one direction. In this circumstance their internal fields become aligned and a strong, permanent, magnetic field is created.
Different compounds have variable capacities for storing the magnetic field.
Mafic rocks like those found at the Crater of Diamonds State Park near Murfreesboro, Arkansas contain small amounts of iron and magnesia which are weakly magnetic. Rocks such as magnetite and jacupirangite contain large amounts of iron and become strongly magnetic when exposed to external magnetic fields. The ring dyke intrusion at Magnet Cove, Arkansas has strongly magnetic signal. These two areas are surveyed by students using a Bison proton precision magnetometer. A model is constructed of the resulting magnetic anomalies.