Description: A piece of lodestone.

Pick up a small needle with the stone.
Hang the stone from the overhead projector by means of thread and tape and bring a bar magnet near it.
Hold the stone near an overhead projection compass. Demonstrate that the stone has a north and a south pole.

According to A Dictionary of Science Oxford University Press:

magnetite
A black mineral form of iron oxide crystallizing in the cubic system. It is a mixed iron(II)-iron(III) oxide, Fe3O4, and is one of the major ores of iron. It is strongly magnetic and some varieties, known as lodestone, are natural magnets; these were used as compasses in the ancient world.

Cautions:

Concepts demonstrated:

Setup Time: Short

Difficulty/Commitment: Straightforward

Visibility: use on the overhead projector

Related demonstrations:

References: PIRA 5G10.15