Extinct Turtle Shell
This turtle shell is supernaturally resellient. Perhaps if you collected all the fragments, you could assemble a powerful protective device.
Turtles are ancient creatures that have changed little over the eons. There are three main categories: sea turtles, land tortoises and fresh-water-dwelling terrapins. This shell is probably from a tortoise, though it is nigh impenetrable and would make a fantastic, if slightly silly, shield.