Murphy turns his considerable talents to the concept of classification in this MathStart title. When Josh receives a strange rock from his uncle, he consults an expert, shop owner Dave, to learn about his gift. He also notices the store's display window, which features stones arranged by size. As Josh's interest in and knowledge of geology grows, the window display changes, with the classification scheme becoming more complex—from size to color to type, and finally to hardness. Murphy's forte is explaining complex topics in a down-to-earth manner, and that's just what he's done here. Along the way, he also includes a good deal of information about rocks, minerals, and the scientific method. Smith's full-color illustrations capture the excitement of rock hunting and include many geological and equipment details. A good introduction to primary geology units or lessons on classification. Activity suggestions for adults and kids are appended.

—Kay Weisman, 5/1/00
Used with permission from Booklist. Copyright © 2000 American Library Association. All rights reserved.

When Amy and Josh begin a rock collection, their friend Dave shows them way to organize their rocks: by size, place of origin, color, the process that formed them, or hardness. Although the unsuspecting will think they are learning only about rocks, the topic of classification is thoroughly explored and is extended with activities for adults and children at the end of the story. Loose color cartoons keep the tone light.