No, actually it's just stone that is part quartz and part something else I can't identify. With this one, as with 'Stone Girl' and others I haven't posted yet, stone provides the matrix on which the clay is 'sculpted.'
I'm pretty bummed these don't scan well. The clay face extends to the stone, but you just don't see the blend unless you're holding the thing in your hand. Guess I'm going to have to get a camera to capture the effect.
Since it's polymer clay, it isn't so much fired as baked. It only takes 275 degrees at 15 minutes to harden. After baking, it's not 'fixed' into the stone. I pop it out, mix up a little JB Weld, stick it to the back of the clay and fit it back into the stone. Once set, I add some more polyclay to blend the rock and the clay, then bake one more time.