How can igneous rocks act as a fossil compass

As the magma cools, magnetite particles in it line up with the Earth's magnetic field and become fixed in position in the resulting rock. These magnetite particles are like tiny fossil compasses ... Changes in magnetic polarity are preserved in rocks of the ocean crust.

Igneous rocks

Explanation:

Magnetite particles in it line up with the Earth's magnetic field and become fixed in place. The magnetite particles act as small fossil compasses