my 6 year old has recenly got into rocks and fossils so I wanted to buy him a book on the subject. I looked at 2 books- this one and the Usborne Naturetrail book "Rocks & Fossils". I chose to buy this DK book but have since bought the other one as well since I did not feel that this was comprehensive enough. This book does have one very good element - it has fold out wipe clean covers showing over 100 different rocks and fossils and the places you are likely to find them so is a good guide to take out with you to help identify your finds, but is is mainly an activity book. There are about 23 different activites & experiments to try at home and when out & about which does not leave much room for information about the rocks themsleves and how they are created. This is where the Usborne book coems in (see my review of that book on its own page).
In conclusion, if you want a reference book, buy the Usborne book first. This does however make a very good companion to it and would be a good buy for some school holiday activities.