The Stone of Erech

There are some additional details about the stone besides what is published in Return of the King. I believe History of Middle-earth volume 8 (War of the Ring) has some more information.

Thank you Mr Underhill. Hmmm - that reminds me. There's an index somewhere ...

In its earliest draft, I think the "Stone of Erech" was a palantir located at Erech. Later, that changed to there being a palantir located at Erech, with the "Stone of Erech" becoming a distinct stone, separate from the palantir, and thus becoming the forerunner to the one in the final published LotR. Eventually reference to the palantir at Erech was removed entirely. As Mr. Underhill says, these drafts are in War of the Ring, Volume 8. A very brief explanation of the Stone of Erech's transition in draft is actually in the HoMe Index as a note on the variability of terms (i.e. "Stone of Erech" could refer to both the original concept of the palantir and also the later concept of the black stone we all know from the final version)

Also just in case it is interesting now or down the line, Tolkien discusses the etymology of "Erech" in Carpenter's Letter #297 (J.R.R. Tolkien to Mr Rang, August 1967)