What are Urim and Thummim?

The Urim and Thummim appear quite early in the book. They are a pair of stones that are given to Santiago by the king Melchizedek. The stones themselves are not large, and Santiago often takes them in and out of a pouch or a pocket. One stone is white, and the other stone is black. The colors represent "yes" and "no." Before giving Santiago the stones, the king tells Santiago that in order to find the treasure, Santiago must follow the omens.

"In order to find the treasure, you will have to follow the omens. God has prepared a path for everyone to follow. You just have to read the omens that he left for you."

Santiago remembers something about omens that his grandfather told him, and the king practically reads Santiago's thoughts. The king realizes that Santiago might need some help interpreting the omens in order to know where to go or when to go. Melchizedek then gives Santiago the Urim and Thummim stones and tells Santiago that they will help with the omens. The king then specifies that Santiago is to ask the stones objective questions and to try to use his own decisions whenever possible.

"They are called Urim and Thummim. The black signifies 'yes,' and the white 'no.' When you are unable to read the omens, they will help you to do so. Always ask an objective question."