"Plastic" Nokia Phones

After a very dusty week backpacking through Utah's Grand Gulch, the power button on my Lumia 1020 stopped working. I ordered a replacement back containing the button strip. I was surprised to find that the plastic on my 1020 was somewhat superficial over a metal frame.

The lighter gray material is all metal

!http://i.imgur.com/XVbUX5A.jpg!