http://photobucket.com/albums/y80/DaBaum/steine/
1st one is just a simple mid-grey granite stone. Most painters I have seen painted their stones like this:
The 2nd is a dark-grey version of the granite:
3rd one is a bright-grey granite:
But how would a standard grey look like with some scratches on it?
Or a dark grey, weather-beaten rock? Note the worn-out edges: