concept

Magnetite

A naturally magnetic iron mineral (an iron oxide). In animals that navigate by magnetic field, sub-micron crystals of magnetite sit inside specialised cells and act like tiny compass needles: as the field changes they rotate or deflect, tugging on the nerve endings around them and sending a mechanical signal to the brain. Unlike the quantum compass in the eye, which gives direction, the magnetite system is thought to read the local field intensity - the information that tells an animal where it is, not just which way it faces. Sturdier and cruder than the radical-pair mechanism.