I second Firith on the bad lighting. Check the Marmoset website they have a nice tutorial about lighting your character/asset. The normal map doesn't work at all. It looks like you just threw you diffuse in Crazybump and that was it. At least make a clean highpoly and bake it on your low to have nice edges and then…
Yeah, I'm pretty sure either your normal map is not rendering, or the lighting just isn't there to pick out the details. Also, your diffuse is smeared out. A property of stone is that while it can have little in the way of color variation, there are often well defined shifts in that color. For example take a look at the…