I tried using a few different sizes of hooks, but settled with a G size hook because I like my stitches tight. However, that made it all the more difficult since the plastic doesn't slide as nicely as yarn does. Nonetheless, here was the result:
I was kind of impressed with the marbled look of the yarn (the black and white effect). But then, on second though, why would I want something crocheted to look like a rock?
I think I'll stick with yarn!