The Emerald Tablet of Hermes Trismegistus is based on authentic Hermetic Teachings and is actually just a short and concise text that can be traced back to a 7th - 9th Century Arab Treatise called Kitab Balaniyus al Hakim fi'l-'Ilal (The Book of Wise Balanis on the Causes).
Please do not confuse Hermetic Science with charlatans like Maurice Doreal who wrote the Emerald Tablets of Thoth the Atlantean.
Maurice Doreal claimed that in 1925, he went to the Great Pyramids of Giza and discovered the Emerald Tablets of Thoth, a king of Atlantis (not to be confused with Emerald Tablet). He then claimed that he had "translated" the text.
In around 1930, Doreal formed the Brotherhood of the White Temple in Denver, having been involved in Theosophy. He claimed that in 1931, in Los Angeles, he met two Atlanteans who took him to a cave underneath Mount Shasta. Doreal quickly developed a cosmology focused on the inner earth, describing "underground races" he claimed to have learned about from the Atlanteans. Doreal developed theories of an underground serpent race. During the 1950s, Doreal incorporated aliens into his views. He combined these all into a theory that in the second half of the 20th century, the serpent race would ally with the Antichrist. He believed that there were "three types of flying saucers including one piloted by 'serpent people' who were once ice-bound in Siberia, became defrosted and then replaced and overthrew the Communist regime in Russia".