They are absolutely of no use to anyone. Send them to me and I will dispose of them properly.
Or you could learn to sharpen your knives with them. You do have knives?
They probably need to be flattened if they have been used much. You can do that several ways. The manufacturer recommends using a diamond plate to rub the stone flat. If you have a nice government supplied concrete sidewalk that will do nicely, just not as quickly. Most any large flat surface will do to a degree.
I have found oil stones at boot sales that were saturated with dried oil. A lost cause unless you know to soak them in solvent to remove the oil. Diesel fuel, mineral spirits, turpentine or something stronger may be required.
As to your broken piece, I don't know how small it is but I find uses for most pieces. You can shape it round to hone the inside curve of carving knives or bond it to a handle to use for an ax or machete.
