This dichotomous key was adapted from various dichotomous keys I've seen around, but edited in response to student feedback. It's easy to use, and can be used to identify 20 different common rock types.
The large size gives students enough space to put the rocks ON the flowchart as they work. It's also great for working with a partner or in a small group.
A reminder of necessary supplies, and safety tips are included on the key.
You could also have students color code it to show Sedimentary, igneous and metamorphic.