Why is my Two year old Herman tortoise recently started chewing on stones and rocks?

No one really knows why turtles will chew on rocks - some think it is because they are bored - make sure you rotate the fixtures in the cage on a regular basis to stimulate the turtle. Some turtles also may use rocks to assist in filing down their beaks so check yours to see if it has larger than normal growth - you should see the vet to take care of this if it is impeding the turtles ability to eat. Also make sure the turtles diet has calcium, chewing on rocks may be a low diet of necessary minerals - remember that reptiles need UV light to help absorb calcium from their foodand sustain good growth.