Some believe it was forged in Atlantis more than 12,000 years ago by star- beings bringing spiritual power to the earth. It has been linked with the Great Pyramid of Giza and the Bermuda triangle, and draws a constant stream of visitors anxious to experience its psychic power.
Since its arrival in the Department of Ethnography at the British Museum at the turn of the century, the remarkable life-size rock crystal sculpture of a human skull - one of only a handful in the world - has provoked constant controversy.
The British Museum bought the skull, allegedly from Mexico and dating from the Aztec period (about ad1300-1500), in 1898 from Tiffany's, the New York jewellers, and it was instantly claimed as genuine by anthropologists.
The most impressive feature of the skull, which has a perfectly smooth cranium and circular eye sockets, is the lack of any identifiable modern tool marks. Thought to be female, the skull, fashioned from a lump of pure quartz, bears a strong resemblance to smaller Aztec and Mixtec stone masks and deities. Rumour has it that cleaners in the museum are afraid to work alone in the room where it is kept.
The only other confirmed crystal skull belongs to the private Mitchell-Hedges collection in Canada. Its origins have been linked to the Mayan civilisation that flourished in Honduras and the Yucatan peninsula of Mexico in the tenth century ad.
However, this skull has a perfectly detachable lower jaw - a fact that must ring warning bells in even the most gullible crystal mystic. While the skulls show a close likeness, Lady Mitchell-Hedges always refused to say how or where she obtained the skull.
While doubt has grown as to their real age, the lack of any sign of how they were manufactured - for example, scratch marks from tools - has been taken as proof of their authenticity.
Now all this has changed. Earlier this year, the British Museum skull was examined by a group of scientists to determine its true origin. The skull was studied in minute detail using a high powered endoscope similar to those used in medical examinations.
The endoscope revealed small cuts on the teeth inside the skull that could only have been made by a steel tool, and provide the first clear evidence that a machine, probably a jeweller's wheel, was used in its construction.
Doubt as to its origin in Mexico arose during an examination of tiny bubbles of liquid and gas trapped in the quartz. These tiny fluid inclusions, present in all rock crystal, can be used to trace where the quartz making the skull came from.
According to Andy Rankin, fluid inclusion expert at Kingston University, the pattern of trails made by the fluid inclusions suggests that the quartz from which the skull was made did not originate in Mexico. The only Latin American source of such rock is in Brazil, several thousand kilometres to the south.
"The inclusion pattern is very distinctive of quartz that formed in ancient rock, billions of years old. No such rock exists in Mexico," said Professor Rankin. "As there is no archaeological evidence to suggest that the Aztecs ever got to Brazil, this new evidence brings into question the authenticity of the skull". Brazilian quartz first appeared as gems in Europe and north America in the mid-19th century, brought back by miners prospecting for gold and silver.
According to Liz Carmichael, assistant keeper at the British Museum, this in about the time when the first rumours of glass skulls started to circulate.
"The authenticity of such artifacts has always been difficult to establish". But, as Dr Carmichael points out, "even if we can prove that the skulls are not from Mexico and date from after the Spanish conquest, we are still none the wiser as to who made them".