A permanent magnet is a magnet that is permanent, in contrast to an electromagnet, which only behaves like a magnet when an electric current is flowing through it. Permanent magnets are made out of substances like magnetite (Fe3O4), the most magnetic naturally occurring mineral, or neodymium, a powerfully magnetic synthetic substance. The alloys from which permanent magnets are made are often very difficult to handle metallurgically. They are mechanically hard and brittle. They may be cast and then ground into shape, or even ground to a powder and formed.