are there any laws protecting a family heirloom that is given as an engagement ring in the event of divorce

my brother proposed to his wife in the outer banks in 2005. he proposed with a diamond that had been cut by my great grandfather in poland in world war II. My grandmother gave it to him to propose to her. She was made aware of the status of the diamond when she accepted. they were married in november 2006 and are currently beginning proceedings for a divorce. he is trying to be amicable and has asked for the diamond-NOT the ring back. she has removed it from their home and hidden it at her mothers. they reside in springfield, PA and were married there as well.