History
In 1823, Smith said that an angel Moroni told him of the existence, with the plates, of "two stones in silver bows" fastened to a breastplate, which the angel called the Urim and Thummim and which he said God had prepared for translating the plates. His mother, Lucy Mack Smith, described them as crystal-like "two smooth three-cornered diamonds." Oliver Cowdery said the stones were "transparent". Smith and his early Mormon contemporaries seem to have used the terms "seer stone" and "Urim and Thummim" interchangeably. Although Smith always referred to the Book of Mormon "interpreters" as the Urim and Thummim, he may or may not have intended to make a distinction between that device and the seer stones that he used in receiving revelations.
In 1827, Smith said that he had been visited again by the angel who had previously revealed the location of the Gold Plates, along with other items such as the Urim and Thummim, and that these objects were buried in a nearby hillside. Smith said that after translating the Book of Mormon, he returned the plates and the Urim and Thummim to the angel, whom he identified as the resurrected Moroni. Joseph Smith reportedly told Orson Pratt that the Lord gave him the Urim and Thummim when he was an inexperienced translator but that as he grew in experience, he no longer needed such assistance.
The LDS Bible Dictionary defines the Urim and Thummim as "an instrument prepared of God to assist man in obtaining revelation from the Lord and in translating languages." In the Book of Mormon, the prophets the Brother of Jared and Mosiah both used devices called "interpreters" to receive revelation for their people, and the Doctrine and Covenants declares that these "interpreters" were the Urim and Thummim.
A 21st-century artistic representation of the Golden plates, Urim and Thummim, Sword of Laban, and Liahona