Seer stone referred to as a key.  All should have one.

"A short time before the house was completed, a man by the name of Josiah Stoal, came from Chenango County, New York, with the view of getting Joseph to assist him in digging for a silver mine. He came for Joseph on account of having heard that he possessed certain keys, by which he could discern things invisible to the natural eye." (Lucy Mack Smith, Biographical Sketches, 1853)