I have had quite a difficult time modeling a convincing rock tower for a tropical island scene (like the rock towers you might see off the coast of Thailand). I thought scanning a real rock might be better. This is a scan of a quartz boulder from my backyard made using Agisoft Photoscan. The rock could easily pass as limestone, or maybe granite if you play around with the texture. The demo vegetation is simply a green sphere distributed by particles/weight map (easy to remove).
Please feel free to use the model/texture as you see fit, btu please let me know if you find the model helpful. Also please let me know if I should scan more of my backyard!