Building A Fire Pit?

I've heard that you should not use River Rock because they will explode when heated. I was given a 20" round sch. 80 pipe that I sunk into the ground about a foot. With about 2 feet above ground. It works great and I was able to buy a grill from Home Depot that fit the top of it. The grill prevents burning chips from blowing out. I did have to drill some air holes along the base of it. I use it even during the summer. (My husband thinks I'm nuts when I do that)