Ferrofluid is a mesmerising fluid coated in magnetite that provides an amazing display when magnetised by magnets. It is commonly used for science and education purposes to give a visual representation of how a magnetic field interacts with ferromagnetic materials. These are also commonly used for cool desk displays, giving office workers the perfect tool to keep their hands busy.
Ferrofluid is made from very small particles coated in magnetite; one of the main iron ores that is highly ferromagnetic. In it's normal state, ferrofluid behaves like a liquid. But if you put a magnet within range of the fluid, the magnetite particles are magnetised and move freely through the liquid, giving a mesmerising kinetic display.