I've hung something similarly irregular by getting a small plate hanger from the dollar store. It has tiny rubber tubes on the hooks that will protect the edges of the stone. The grips are on springs so it will self adjust to an irregular shape. I was worried the grips hanging over the edge would bother me, but they don't. It's been up for two years without issue. This one in the picture is from Michaels and should do the trick... it will set you back a whopping $2.69.

There is something they have come out with recently may be by 3M that is sticky and can hold up heavier items..maybe someone else can help in this regard, but I would be tempted to make it into even more of a feature by placing on a rustic barn wood shelf and use sticky stuff or Velcro to keep it from sliding off.