For studying rocks, I felt this was a great introductory book. The pictures are clear, up-close, and interesting and the text is easy to understand. I really love how they bring out the many benefits that rocks bring the earth including that they store water and affect weather - two things that other books of this level don't go into.
My one complaint about this book is that in describing the three different types of rock they listed "volcanic", sedimentary, and metamorphic. I don't understand why they couldn't use the scientific name of igneous instead of volcanic. They mention that "igneous" is the other name for volcanic rocks, but come on! They say sedimentary and metamorphic, why not throw in igneous - which is what they're called. I never learned to call them "volcanic" rocks, they were always igneous. They don't give kids enough credit, I think.
Overall, this book is great, and I was able to overcome the silly "volcanic" word by self-editing and saying "igneous" while reading the book to my son.