Rocks
Damn, long link.
But that's an example of what I mean. Ignoring the texture (because that really won't be what makes your stones look real), look at the way the shadows play across the rock. Following the shadows are edges of hard light. Using high contrast with light and shadow will give you a more realistic texture than if you use a texture on top of your shading.
Stone Tile
Those are good stone tiles. Having some variety between the tiles would be good, especially if you make tiles beside each other less obviously mass coloured. Real tiles don't fit together perfectly - characteristics in the stone do not continue into the tiles beside them.
Shadows and lighting, a gain, will help make it more real. Depending on where your light source is (and if you want your tiles to be raised, with some space between them), light will appear on the edge of the tiles because of the angle we see it at.
I wish you luck with finishing your picture.