At what point did Joseph Smith’s peep stones become the Urim and Thummin?
You’ve got it backwards. The Urim and Thummin, which is a very ancient instrument prepared by God to permit his prophets to interpret lost languages, was given to the Prophet Joseph Smith along with the original record now known as the Book of Mormon, to enable him to translate it into English. “Peep stones,” as they were called, were not unknown at that time, but were associated with witchcraft, and used to deceive people into believing whatever the witch conjured up while gazing at the pebbles. Some of the detractors of the Prophet, of whom there were many, accused him of using “peep stones,” not realizing or caring to realize that he was in possession of a sacred instrument placed in his hands by an angel of God.
Both Francis W. Kirkham and Elder Bruce R. McConkie have written authoritative comments on the subject, as follows—
“Mineral rods and balls, (as they were called by the impostor who made use of them,) were supposed to be infallible guides to these sources of wealth-”PEEP STONES” or pebbles, taken promiscuously from the brook or field, were placed in a hat or other situation excluded from the light, when some WIZARD or WITCH (for these performances were not confined to either sex) applied their eyes, and nearly starting their balls from their sockets, declared they saw all the wonders of nature, including of course, ample stores of silver and gold” (Francis W. Kirkham, A New Witness for Christ in America, 2:, p.69).
“In imitation of the true order of heaven whereby seers receive revelations from God through a Urim and Thummim, the devil gives his own revelations to some of his followers through peep stones or crystal balls. An instance of this copying of the true order occurred in the early days of this dispensation. Hiram Page had such a stone and was professing to have revelations for the upbuilding of Zion and the governing of the Church. Oliver Cowdery and some others were wrongly influenced thereby in consequence of which Oliver was commanded by revelation: “Thou shalt take thy brother, Hiram Page, between him and thee alone, and tell him that those things which he hath written from that stone are not of me, and that Satan deceiveth him” (Doctrine & Covenants 28:11.). (Bruce R. McConkie, Mormon Doctrine, 2d ed., p.565)