Magnetite is a type of iron oxide with natural magnetic properties. In fact, it is the most magnetic natural mineral on Earth and was once used in compasses. Its chemical name is ferrous-ferric oxide and its chemical formula is Fe 3 O 4 .
Magnetite was used by ancient civilizations to magnetize compass needles.
This mineral occurs in almost all igneous and metamorphic rocks, although usually only in small particles or in a solution with other minerals. Some beaches, often called black sand beaches, have heavy deposits of magnetite. There are also significant and concentrated deposits of hematite, a mineral resulting from the reaction of magnetite with oxygen, in very old sedimentary rock formations known as banded iron formations.
The naturally occurring magnetite in the brains of some animals is hypothesized to allow them to sense the Earth’s magnetic field.
In addition to geological formations, magnetite is found in small amounts in certain bacteria and animals. Chitons, a type of mollusk, have the crystals on their radula, a scraping appendage used for eating. These crystals make the radula very abrasive, allowing chitons to scrape food off rocks.
Magnetite occurs naturally in the brains of some birds and insects, particularly bees, and even humans. The hypothesis is to allow a sense called magnetoception or magnetoception, through which the animals in question have a natural sense of direction. Biomagnetism can allow animals to sense the Earth’s magnetic field, in the same way that a compass uses magnetism to indicate cardinal directions. For example, crystals in the brains of certain birds can help trigger and direct their migratory flight when the seasons change.
Evidence of the first compasses using hematite dates back to 1000 BC.
Humans realized the magnetic properties of lodestone and its navigation possibilities early in their history. There is archaeological evidence that the Olmecs of ancient Mexico developed a rudimentary compass using hematite around 1000 BC. The attractive properties of magnetite, a particular crystalline formation of magnetite, have been mentioned in Chinese literature dating back to the 1st century CE, and the Chinese were using magnetized needle compasses by the 11th century. Europeans started using a similar device a few decades later than the Chinese, and it is unknown whether or not it was independently developed.