Its an electro-magnet -

currents flowing through the iron core.

With a waterjet.

alot

A magnet ie. the the ones on your fridge are made by manufactures pushing electrical current through ferrous metals causing them to have magnetic properties. Rare earth magnets are naturally occurring elements that have magnetic properties by themselves.

Granite can be slightly magnetic. If you bring rare earth magnet towards it, the magnet attracts. Especially if it is mined from India.

Oxides of iron and titanium are responsible for this.