Those are soapstone rocks, especially useful for keeping a drink cool without diluting it or otherwise altering its flavor. The stones came in a pack of nine, and the box instructed to let them freeze for four hours before use.
I am impressed with the stones. They keep the liquid cool but not overly cold like ice can (which would numb the tongue to some of the whisky's flavors). In fact, I thought the stones brought out the best of the Glenlivet 12 I tried them with, which seemed just a little smoother and tastier than usual. The stones are fashionable too. Highly recommended!
* Okay, feel free to kill your Dewar's or Famous Grouse with as much as ice as you want.