National Geographic  Pocket Guide to Rocks and Minerals of North America

Rather than collect shells, rocks and other natural objects, consider taking photos or drawing a sketch instead and let the objects stay where they are. The Leave No Trace principle of "Leave What You Find" ensures the next visitor will experience the same joy of discovery you have and permits valuable, sometimes imperceptible, materials (such as the minerals in shells) to stay in their ecosystem for future plants and animals to use.

From the publisher:
In a logical, user-friendly, highly visual format, this pocket guide—one of an expanding collection of National Geographic pocket guides—offers key facts about dozens of rocks and minerals, how to hunt and identify them, where and how to go looking. The book also pictures and explains the fossils most likely to be found and the fundamental land and rock formations in the North American landscape.

With 160 entries, formatted with clear language, key identification points, carefully chosen photographs, and expertly drafted illustrations, this guide is the perfect starting point for anyone, young or old, interested in the study of rocks and geology.