Look at what Sophie gave me!

Mckayla has a good friend at school named Sophie who she has been talking about constantly since Sophie moved in. On Friday she came home from school all excited because Sophie had given her a present. I small shiny white rock. Only it wasn't a rock. Any guesses?
The girls have been obsessed with rocks since Jake has taken them rock hunting a few times and it is the Tucson gem and mineral show so we got to go up and see some really awesome rocks. We now have a small rock collection growing in their bedroom. Mckayla was very happy to recieve a small white rock from her friend and it even had a certain smell to it....
When I asked where she got it she said that Sophie gave it to her for a present, and when I asked where Sophie got it, she said that Trevor had given it to her....
I had her give it to me and go wash her hands. I didn't throw it away in front of her, but quietly got rid of it at another time. She didn't know any better, as I'm sure Sophie and Trevor didn't either. So, any guesses as to what it was??? The answer will be revealed in the comments section in a little while.