Floating rocks/islands are one of most favourite things in the whole world (well at least in my fantasy world). I have always wanted to build one for my minis. It is people like you, that make me envious that you ALREADY have one. Yours is one of the better ones that I have seen.
I especially like the fact that is anchored to something, and the roots are a really nice too.
Did I mention that the dimensions (relative to the mini) are just perfect. - Let me go back and have another good look at your work.