My dog is chewing on rocks--but she's not a lab!!! Please help!?

My 5 1/2 month old puppy Sweeney Todd loves to chew on rocks. I did a few searches and found it's cmmon--with labrador retrievers. She is a Pomeranian-Chihuahua mix (A pomi-huahua if you will) and she isn't very big. She's ten pounds (weighed today) and is about 33 inches from nose to tail. She keeps finding these rocks and bringing them in the house to chew on them. I keep taking them away so she won't swallow them and choke, but she keeps doing it!!! Can someone please help?!