David Whitmer recounts that one of the BOM translation instruments of the Urim and Thummim were two white stones placed in spectacles.
"Interview with David Whitmer", Deseret Evening News 11, no. 224 (August 16, 1878): 2
I–How did you know Joseph to be at that time?
He–As a very humble and meek man, and very simple minded indeed. He did the will of the Lord, and an arduous task it was to translate the Book of Mormon.
I–Did Joseph use the Urim and Thummim when he translated?
He–The Urim and Thummim were two white stones, each of them cased in as spectacles are, in a kind of silver casing, but the bow between the stones was more heavy, and longer apart between the stones, than we usually find it in spectacles. Martin Harris, Oliver Cowdery, Emma and my brother John each at different times wrote for Joseph as he translated.