Antique Ansonia Mantel Clock

I recently purchased this Ansonia clock from an estate sale. I haven't been able to find another one like it and wondering if anyone knows the model and circa? Also, it's incredibly heavy and it appears that it may be entirely marble, not just the inlay sections, as a magnet won't adhere to it. Is there another way to tell? It also works very well and I have the key but am afraid to overwind. Is there a gauge for knowing how to do this correctly? Help, I'm a novice... Thank you!!