Are you looking for a good, solid instructional activity on sedimentary rocks? This one, produced by the Illinois State Museum, is just such a instructional activity. Middle schoolers identify common rocks and minerals by analyzing sediments from local water sources. There is a meaningful, and easy-to-implement, inquiry described in the plan. Additionally, some terrific extension activities are in place. The worksheet that is mentioned in the plan does not seem to be present, but that can be easily produced by the teacher.