Basic Rock Identification
Around here we rarely find rocks made of a single mineral that we can identify through color, luster, streak, hardness, and cleavage, but you can classify rocks into their three basic classes: igneous, metamorphic, and sedimentary.
All you need is one hammer and goggles for everyone participating. A geologist's pick hammer is most effective though this can be done with other hammers. And you need to find a flat, hard surface on which to do the cracking.
You can play the Rock Type Game at Geology For Kids as a warm up. You can also read the classic A First Look At Rocks by Millicent Selsam, or DK e.Guides Rocks and Minerals to get an idea what to look for when classifying them.
Cracking them open, as well as wetting them, really helps to see crystals and layering. And I didn't have to ask twice if anyone wanted to do this activity. For older kids, have them try to identify the specific types in each category. They can also map the location of their rocks, and see if different locations have different predominant types. The Moh's hardness scale is helpful for this, especially the hardness of common items you can use to test your samples. For advanced students, check out the igneous rocks, metamorphic rocks, and sedimentary rocks classification pages.
These two rocks are the same specimen. The picture doesn't show how much more lustrous the inner rock is compared to the worn outer surface.
It's granite, an igneous rock.