Maybe the rock is special, maybe its just a rock. Ultimately the only important part is whether or not it's special to you.
You may feel energy given off by the rock although it's quite likely that your own belief in it has subconsciously attached your own energy to it. It really doesn't matter what the rock is, if it means something to you then keep it and use it, the world is full of objects just like that. In my own faith the Lia Fail is an incredibly sacred rock, it is though just a rock, it's the energy and belief that has been attached to it that gives it both its meaning and power.