For that May birthday: May's birthstone is the Emerald - Emeralds are one of the most beloved of gems, with a colorful and long history, earning it the rank of "precious" stone, along with diamond, ruby and sapphire. The Emerald, a symbol of rebirth, is believed to grant the owner foresight, good fortune, and youth.
http://www.irishvictorian.com/store/p110/Birthstone_Claddagh_Ring_-_May.html
http://www.irishvictorian.com/store/p110/Birthstone_Claddagh_Ring_-_May.html