Yes, I baked the stone along with the clay. Gems, minerals, crystals and glass don't get affected by such a low temperature, as the one needed to bake polymer clay. So you can use it without fear, it will not crack, I promise. What you must never put in the oven is plastic, it melts and stinks.
Ah I see! It didn't even look like clay so I was confused! I still need to buy myself some sculpey and do some clay work since you requested it >.<' I just haven't been able to get down to the store for it. I have no idea what I would even make it's been so long since I last sculpted.
Ah, once you get the clay on your hands, i'm sure it'll come back to you! I started with the typical miniature sweets everyone does, eventually i found my own style, and now I try to develope that. Can't wait to see what you'll make!