BK6 Field Guide to Rocks and Minerals – National Audubon Society by Charles W. Chesterman – The first all-photographic field guide features 794 full-color images of all the important rocks, gems, and minerals of North America, showing their many variations of color and crystal forms. The text provides descriptions of 200 minerals (including 20 classified as gemstones) and 40 rocks, as well as descriptions of the natural environments where they occur.