HI!
I'm pretty new around here too. I've never tried to read rocks, and I'm not sure you can use a Kindle for that. But that's cool.
I just ordered a "barely used" Kindle in order to get mine faster. Some of the prices there get pretty outrageous, but if you watch the low end, sometimes there are ok prices, too (those go uber-fast, so you may want to practice up with the clicker

).
I'm also still looking at the iRex for my larger dimensioned game book PDF's, but that seems to be even more difficult to get a hold of.