If you need something fun for your students to do, try this. It's creative and educational!

[edit] Steps

Have your students find a medium sized rock. (Bigger than a pebble and smaller than a boulder)
Teach them about the rock cycle and have them find which type of rock it is. If it's Sedimentary, it's Egyptian, if it's Igneous, it's Roman, and if it's metamorphic, it's Greek.
Have them look up information about the rocks' cultures. Then have them name it.
Tell them to decorate their rocks at home to make them look like it once lived in that place.
Tell them to weigh their rocks on a scale, write a story about their rock, and/or create a home.
Create a birth certificate and have them fill it out.

[edit] Tips

If they're painting your pet rock, they can add googly eyes if they want.
If their rock is a unique color you don't have to paint it
The good thing about small pet rocks is that they can carry theirs around at take care of it, when they project is finished.