Fairly good start. You've perked my interest.

I like the way in which all three girls reacted differently to finding the crystals. I especially like that one of the girls even threw her crystal away, like it was just a useless rock. A lot of the times in stories like these, all the characters keep the "unusual magical item" without an explanation for why. So it was good to see mixed reactions from everyone.

There's only one thing that bothers me (don't worry, it's really a small thing). But why are all three girls conveniently born in English speaking countries? I think the story might be a lot more interesting if at least one girl came from a country where the main language wasn't English (if you were to randomly pick three girls from around the world, it'd be highly unlikely that they'd all speak English).

You could still write her dialogue in English or even have English be her second language (just so there's no communication difficulties with the other two girls, or you could even leave the communication difficulties in and have that become a ongoing obstacle in the story that the girls have to work around). In my opinion, it would make the choice of the three girls seem less contrived and more natural, lending believability to their specialness.

Sort of off topic, but I absolutely love the name Amelia.