Find and Collect the Most Sought-After Rocks & Minerals Rock collecting is the treasure hunt of a lifetime, and the Upper Midwest is a wonderful place to start. The region is home to a variety of collectible and valuable specimens of rocks and minerals. From Lake Superior Agates to Petoskey Stone to geodes and fossils, the area's offerings provide a challenge but are possible--and in some cases likely--to be found with the right approach...