Mary Collins's necklace

An amber necklace provided the sorceress Mary Collins with the magical energy necessary to cast various spells and enchantments.

Among these, she used it to perform a teleportation spell that helped her avoid being seized by Uther, a glamour, that she used to take on the form of Lady Helen, and a powerful sleeping enchantment that put the entire court of Camelot to sleep, except for Merlin due to his magic (The Dragon's Call).

Trivia

 * Merlin101_0332.jpg holding her necklace.]]It is possible that baltic amber characterises artifacts of the Old Religion, considering that the Mage Stone itself was made of amber, just as Morgause's ring was.