Jon kept a secret from Karyn, there was a reason he didn't swoon over Sarah like all the other boys did. Jon and Sarah were cousins, their moms were sisters.
Sarah was a bitch at school and in public but when they were alone or with family they got along rather well. In fact Jon was going to tell Sarah about the stone when she came over for dinner, which happened quite frequently due to Mr. McMillan's Job.
Sarah used her key to enter the Gibson house, and headed straight for her cousin's room.
Jon showed the stone and note to Sarah in the same way he had earlier to Karyn.
"Wow" Sarah said "and all I got was his coin collection, I guess you were his favorite"
"Doesn't say that he loved us all equally. Hey, want to make a wish?"
"Ok"
"Be careful. I showed it to Karyn earlier and she messed up"
"Ok, I get it"
I handed Sarah the stone.
"That's what Karyn said"
"Ok I get it let me make my wish"
"Ok"
"I wish I knew why grandpa left Jon the stone and all I got was a coin collection"