What is the black residue on my finger after handling black magnets?

I purachsed a 'Klutz' "Magnetic Magic" book with black magnets included, but using them, my fingers turned black. Is this just magnetite or something more dangerous like lead? The magnets were made in China. I could not find this product on any CPSC recall list but just wanted to make sure. Thanks!|||probably iron|||it's just ceramic dust. Most magnets are made from a ceramic material. It isn;t lead since refined lead is a silver-gray and is not magnetic.|||I think thats IRON ORE