Originally written as a response to an inquiry in a chat.
The Emerald Tablets of Thoth was first published in 1931 by Maurice Doreal and claims to be from an “Atlantian” named Thoth. Right off the bat that’s sending up red flags. Atlantis didn’t ever exist, it was a myth written as an object lesson in a treatise. Doubly so given we see no mention of it before that. We do find examples of civilizations destroyed by floods in ancient literature but not one that matches the description given.
The earliest example I’m aware of is the Sumerian deluge myth. The first five Sumerian cities were said to have been washed away by a flood in a story that the myth of Noah was based on. (see ISBN 978-0-345-80439-6) They were then rebuilt and archaeological sites exist for at least some of them. Flooding was a common issue where they were located and if you look at the archaeological record you can see them moving their cities further and further from the rivers and sea as time goes on to mitigate the issue.
Best I can tell he never produced any tablets as evidence he didn’t just make it all up himself. There are some images that are associated with them of a green tablet, the image attached to this blog post, but I can’t find any information on it. Either way he certainly hasn’t proven they were a legitimate translation of a legitimate text. It’s also an important note that Doreal started the Brotherhood of the White Temple around 1930 and the text essentially served as the holy book for their cult. In short, there’s no evidence to suggest it was in any way historical and therefore can be discarded.
If you’re looking for an emerald tablet that is legitimate checkout The Emerald Tablet of Hermes Trismegistus which seems to be often mistaken for the aforementioned text.