Do you have a kiln and clay?
I do fossil medallions with my 2nd grade class each year. I gather small
shells, leaves, or anything that will leave a good imprint. We form the
clay into round flat disks. The students then press the objects into the
clay, leaving an impression. They then decorate the edges of the medallion
and put 2 holes (so it will hang straight) near the top edge. After the
"fossils" are fired, they coat them with brown shoe polish (the ones with
the foam tops) this makes the impression show up well and gives a shine to
The students love it and we discuss how the clay has been transformed and
how this process compares to actual fossils.