Hi all, I've been stalking the forum forever. I am actually rereading the Mistborn Trilogy now. In HoA it goes on to explain hemalurgy. Vin snapped when her mother killed her sister and her mother was "spiking" Vin with the earring through her sister. Giving Vin a double boost of bronze.
"In The Hero of Ages, Vin's earring is revealed to be a hemalurgic spike. Her mother killed her sister (who was a Seeker) and put it in Vin's ear. This explains Vin's ability to see through most copperclouds. Because Vin wears the earring, Ruin is able to speak with her directly, and does so throughout this book. Marsh eventually recognizes her earring for what it is, and is able to remove it from her ear against the wishes of Ruin, thereby saving Vin's life and enabling her to utilize the Mists." Taken from The Coppermind <http://coppermind.net/wiki/Vin's_earring>
