Magnetite stands out as the most magnetic mineral, possessing a strong attraction to magnets. This magnetic property arises from its unique crystal structure and the presence of iron. Over time, magnetite can undergo oxidation, transforming into maghemite and eventually into hematite. This process often results in a zoned appearance, with a brown exterior and a black magnetite core. Interestingly, maghemite also exhibits magnetic properties.
Beyond magnetite, several other minerals display moderate to strong magnetism, often sharing structural similarities. Ilmenite, a common mineral often found alongside magnetite, is a double oxide of iron and titanium and exhibits magnetic characteristics. Tantalite/columbite, or manganotantalite ((Fe, Mn)(Ta, Nb)₂O₆), while less magnetic than magnetite, can still influence a compass needle. Visually similar to magnetite, it sometimes displays a subtle purplish brown sheen. Chromite, a double oxide of chromium and iron, also possesses strong magnetic properties, typically appearing black. Franklinite, a complex oxide of zinc, iron, and manganese, belongs to the magnetite group and exhibits a reddish-purple hue along with magnetic attraction.
Numerous other minerals within the magnetite group exhibit weaker magnetic properties, many of which are relatively rare. Generally, the degree of oxidation and the substitution of iron with other metals correlate with a decrease in magnetic strength. A noteworthy exception is platinum, a metallic mineral that exhibits weak magnetism. Finding magnetic, metallic sand could indicate the presence of this valuable metal.
