THE MAGNETIC MINERALS

The Magnetic Minerals are few, but the property is important because of this fact. Once a specimen is established as magnetic, identification becomes a rather routine exercise. The mineral magnetite is named after this characteristic.

Magnetism occurs (most often) when there is an imbalance in the structural arrangement of the iron ions. Iron is found in two principle ionic states called ferrous and ferric ions. The ferrous ion has charge of positive two, (+2); the ferric ion has a charge of positive three, (+3). The two ions have different atomic radii because the higher charge of the ferric ions pulls the electrons surrounding the ion in tighter. This fact can lead to the different ions being placed in separate positions in a crystal structure. Electrons that move from the ferrous to the higher positively charged ferric ions create a slight magnetic field.

The minerals that are magnetic range in magnetic strength from being capable of lifting steel rods to barely turning the needle on a compass. A few minerals may not be magnetic, but are still attracted to magnets. Magnetism is somewhat of an unreliable property as not all specimens may demonstrate it. While the presence of magnetism may all but clinch an identification, the lack of magnetism should not generally exclude typically magnetic minerals. A compass needle is a good test device for testing magnetism as is a magnet on a string that might sway near the specimen.