Rocks in His Head by Carol Otis Hurst
Ages 4-8. 32 pages. A biographical retelling of a man who always loved rocks until one day he's offered a job in a museum, even though he doesn't have a college degree.
Basher: Rocks & Minerals: A Gem of a Book by Dan Green
Ages 9-12. 128 pages. Three interesting facts, a short description, and a list of basic facts (chemical formula, hardness, etc.) are provided about each rock in this book that uses a first-person, conversational style in its writing.
Rockhead by Brian Kure
Ages 6-10. 32 pages. After a freak accident, a boy discovers his geologic powers that will save his town.
Journey to the Center of the Earth by Jules Verne
Ages 9-12. 128 pages. In this abridged, Treasure of Illustrated Classics version, kids can travel with Verne's characters from Iceland to the Earth's core and back up again, through a volcano.
Smithsonian Natural History by DK Publishing
Ages 10 and up. 648 pages. More than just about rocks, minerals, and fossils; this book is a visual encyclopedia of natural history.