Dimeritium

(Polish dwimeryt)

Source

 * Tower Mage's Book

Game trivia

 * Triss Merigold gave Alvin a dimeritium amulet to help the boy.
 * Jacques de Aldersberg wears a dimeritium pendant under his armour and clothes.

Of note

 * Vilgefortz of Roggeveen was shackled with dimeritium after he was found guilty of treason.

Dwimeryt