How can I achieve this look with fondant?
It looks like granite, stone with little white dots, don't want to use edible image.
I would use a stippling brush and the colors dark gray, gray and a little white. If you don't know what stippling is you can google or you tube it. It involves a stiff brush and watered down colors. Instead of brushing the paint on, you pounce the brush on the suface in the different shades of your choice. You should get a good effect. If you google, you will find that this technique is used for stippling walls but you will get the general idea.