What exactly is a gem? How is it used, besides in jewelry? Gems are some of Earth's most precious resources, and some of them are millions--or even billions--of years in the making. In this instructive volume, readers learn about the incredible processes that take place under the surface of Earth to form different kinds of gems. Gorgeous photographs pair with the accessible text that covers both gem mining and lab-created gems. Sidebars and fact boxes add even more information that supports science classroom learning.