Magnetite is a naturally occurring magnetic mineral found in igneous and metamorphic rocks, as well as in some animals and humans. It is hypothesized to enable a sense of magnetoreception. Humans have used it for navigation since ancient times.
Magnetite is a type of iron oxide with naturally occurring magnetic properties. In fact, it is the most naturally occurring magnetic mineral on Earth and was once used in compasses. Its chemical name is ferrous-ferric oxide and its chemical formula is Fe3O4.
This mineral is found in nearly all igneous and metamorphic rocks, though usually only in small particles or in a solution with other minerals. Some beaches, often called black sand beaches, have heavy lodestone deposits. There are also significant and concentrated deposits of it and of hematite, a mineral resulting from the reaction of magnetite with oxygen, in very ancient sedimentary rock formations known as banded iron formations.
In addition to geological formations, magnetite is found in small quantities in some bacteria and animals. Chitons, a type of mollusk, have 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, especially bees, and even in humans. It is hypothesized to enable a sense called magnetoreception or magnetoception, through which the animals in question have a natural sense of orientation. Biomagnetism may allow animals to sense the Earth’s magnetic field, much like a compass uses magnetism to indicate cardinal directions. For example, crystals in the brains of some birds may help trigger and direct their migratory flight as the seasons change.
Humans realized magnetite’s magnetic properties and its navigational possibilities early in their history. There is archaeological evidence that the Olmecs of ancient Mexico had developed a rudimentary compass using hematite around 1000 BC. The attractive properties of lodestone, a particular crystalline formation of magnetite, have been mentioned in Chinese literature dating back to the 1st century AD, and the Chinese they had been using magnetized needle compasses since the 11th century. Europeans began using a similar device a few decades after the Chinese, and whether or not it was independently developed is unknown.
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