And in the breastpiece of judgment you shall put the Urim and the Thummim, and they shall be on Aaron's heart, when he goes in before the LORD. Thus Aaron shall bear the judgment of the people of Israel on his heart before the LORD regularly.
Exodus 28:30

Josephus wrote that one of the High Priest's divining stones (the urim and thumim) used to shine in God's presence, but it stopped about 100 years BC. Is this true? Nobody knows. Nobody knows much of anything at all about these two stones.