Can you give some more info on your find? Place a soda can or coin next to it to show size and proportion in the images. There are a few things you can do to narrow it down. Research... Does a magnet stick to it? Are there other smaller pieces in the area? Is magnetite common in the surrounding geological landscape? Test for nickel iron.
Without knowing the answers to the previous questions its hard to make a guess. There are other ways to find out but start with that. Have you had any luck or any updates