I think it's pretty good as-is. It lets you blow up some rocks for free, if you already had bombs, since it'll just drop another. There might be some goodies at the other side of the bomb rock.

Chain reactions, and the chance for a 1+1 free bomb, is a great bonus.

I can't really think of what else the trinket could do that maintains the theme. Maybe a chance for a tinted rock to drop an extra soul heart? Or maybe, give all the rocks a very, very, small chance to drop The Small Rock? Not sure how balanced any of this would be. I'm still very happy with what the trinket does already.

I appreciate that

Maybe have it so that it lets you pick up Sticky Nickels for free? Chip them off of the floor?

Other than that a cool trinket idea. Not overpowered, but has decent utility if you need bombs/have a way to destroy rocks. Would also make items buried behind rocks effectively free.