In Exodus 28, what sacred objects were placed in the high priest's breastpiece?

In Exodus 28, the sacred objects placed in the high priest's breastpiece were the Urim and Thummim.

The chapter describes the breastpiece worn by Aaron, Israel's high priest, as part of his official garments. It held twelve precious stones, each associated with one of the tribes of Israel. Exodus then instructs that the Urim and Thummim be placed inside the breastpiece, close to the high priest's heart.

The biblical text gives little physical description of these objects or explains precisely how they functioned. Later biblical passages associate them with seeking divine guidance. They should not be confused with the twelve stones themselves, the ephod, or the engraved forehead plate. Because the text is brief, later Jewish and Christian interpretations differ about their appearance and use.