Pretty sure I've read that you can in the past. Also I just went and picked some up myself from a landscape yard so I will soon be finding out myself. I think it will make for a nice tank due to all the different shades of color that they come in. I have some nice big 30lb rocks along with a ton of smaller stuff. Maybe we can compare pictures when and if you go this route. GL
Found this on the net, searched just to make sure:
There is absolutely no reason not to use granite in a freshwater aquarium. It is typically an inert stone, and will not affect water quality. If you collect it yourself however, make sure you sterilize it by soaking the pieces in hot water, then rinsing thoroughly and allowing to cool before use.
I got mine from a landscape yard, rinsed it with the hose a few times and good to go.
I would also say that granite is safe, it is very non reactive mainly because it is a very old rock. You can test how reactive a rock is by pouring a little bit of vinigar on it, if the vinigar bubbles away on the rock then it means that you might want to think twice about using that rock in the tank.