The Seer Stone referred to here was a chocolate-colored, somewhat egg-shaped stone which the Prophet found while digging a well in company with his brother Hyrum,... It possessed the qualities of Urim & Thummim, since by means of it - as described above - as well by means of the Interpreters found with the Nephite record, Joseph was able to translate the characters engraven on the plates.

Defense of the Faith and the Saints (ed. 1907)