Everyone seems to equate "stones" with the planets, but to me "He keeps watching the stones" sounds like someone sitting in a ship watching a ring rotating.
I would also posit to check any and all asteroid belts. They seem to be the red headed stepchild (no offense, I’m a ginger myself) of mining and I’m gonna bet if FDev wanted to hide something in the Coalsack nebula, they’d put it in one of those.