The crystal skulls are a particularly notable example of the popularization of pseudoarcheological ideas. Some believe the skulls to be of Aztec or Mayan origin, while others think them to be from Atlantis or outer space. Pop Culture references to theses skulls in movies like Indiana Jones and the Kingdom of the Crystal Skulls has brought these sort of pseudoarchaeological ideas in to the forefront. The movie directly engages with the idea that these crystal skulls are associated with aliens which is a long held belife by many. However, archaeologist are largely under the impression that they are fakes made by Europeans. There was a large amount of fake artifacts manufactured in the 1800's which in Mexico which were then sold to unknowing European travelers. More then just crystal skulls were faked and sold off to institutions all over the western world. Pottery was a particularly popular knock off that was sold to gullible European visitors. Moreover, there is solid historical documentation that suggests that Eugene Boban manufactured many of the first crystal skulls, starting the whole mania. The most notable crystal skulls are the Mitchell-Hedges Skull, also known as the Skull of Doom, The British Museum Skull, The Paris Skull, and the Smithsonian Skull.  There is significant empirical data that disproves the authenticity of these crystal skulls. The most significant pieces of evidence against the crystal skulls is that they were likely made using German lapidaries with crystal either from Madagascar or Brazil in the 18th or 19th century. 
None of the known skulls are actually from a documented archaeological sites, nor do they reflect the artistic styles of the cultural groups they are attributed to. The first known crystal skull was obtained by the British Museum in 1856 by Henry Christy. At this time there was little known about pre-Columbian artifacts in Mexico and as observed by Smithsonian archaeologist, W. H. Holmes, in 1884 there was an abundance of fake artifacts being sold in Mexico at the time.  There was an abundance of fake artifacts that made into European museums that are only being revealed as frauds within the past few decades. In 1867 two more crystal skulls surfaced at the Exposition Universelle in Paris. These skulls had been procured by an "archaeologist" named Eugene Boban. Mexico City purchased two crystal skulls; one in 1874 and another in 1886. These skulls account for the first generation of crystal skulls. The second generation of crystal skulls are also associated with Eugene Boban, who in 1881 attempted to sell a crystal skull in his antiques shop in Paris. The skull did not sell so Boban returned to Mexico City in an attempt to sell the skull to Mexico's national museum claiming that it was a genuine Aztec artifact. The Mexican museum declined, however, assuming the skull to be a fake. In 1886 the skull was sold in an Auction in New York to Tiffany & Co. Ten years later Tiffany & Co would sell the crystal skull to the British Museum for the same price it was bought at, $950. The auction's catalog lists another skull having been sold but its current whereabouts are unknown. The third generation of skulls surfaced around 1934 when art dealer, Sidney Burney, purchased a skull with extremely similar proportions to the skull bought by Tiffany & Co. However, this skull was much more detailed and had a detachable mandible. This skull, typically referred to as the “Mitchell-Hedges” skull, is attributed to the Maya instead of the Aztec, is said to emit a blue glow from its eyes, and is said by its supporters to occasionally crash computer hard drives. As time has passed more and more skulls have come forth. There are now what could likely be categorized as fifth or sixth generation skulls. Moreover, they are no longer suggested to be from exclusively Mexico. People claim they have been found all over Central and South America and one was even said to be from Tibet. Many of theses newer "crystal" skulls are not even made of crystal, but rather glass or resin. 
The Mitchell-Hedges Skull, sometimes called the Skull of Doom, is the main source of superstition that surround these skulls. The skull is named after Anna Mitchell-Hedges who was said to have found it at Lubaantun, Belize in 1924. Her father was a British adventurer who was said to have had excavated there. It is said that she found the skull underneath a sacrificial alter. However, there is documentation that states that Mitchell-Hedges bought the skull at an auction in 1943. Anna Mitchell-Hedges asserted that it had been theirs and it was put up to auction against their will forcing them to buy it back. Anna encouraged the notion of the skull having mystical powers. She toured North America with it, showing it off to notable figures including Church of Satan founder Anton Szandor LaVey, Native American poet Paula Gunn Allen, actress Shirley McLaine, and the mediums of Lily Dale, a Spiritualist community in New York. The skull in this way was able to gain notoriety and infamy. 
The popularity of these crystal skulls has greatly increased due to their inclusion in Indiana Jones and the Kingdom of the Crystal Skulls. The popular movie depicts the skulls as belonging to aliens which is a notion deeply rooted in pseudo archaeological thought.  In this way, the depiction of the skulls in this most recent installment of the franchise is highly damaging to the field of Archaeology. This movie depicts the indigenous people as generic savages, much too simple to create the skulls themselves and instead suggests that the skull belongs to the body of an alien. This is not a new concept. Aliens have been linked to the crystal skulls for several decades.
Another prevalent pseudoarchaeological idea about the origins or the crystal skulls is that they originate from Atlantis. Edger Cayce, born in 1877, is a prominent figure in this argument. Also known as the sleeping prophet, Edgar Cayce was known to go into trances and awake with new knowledge, which was often connected to the lost continent of Atlantis. He belivesd and taught that people were reincarnated and would often track peoples past lives to Atlantis. Cayce was a hyperdiffsionist who believed that all of the world's culture diffused from Atlantis. It is proposed by those who beive in this, that crystals helped heighten Atlantian's physic abilities allowing them to see into other dimensions. Moreover, the crystals were reportedly used to power the machines that Cayce saw in his visions. When the crystals were brought to Central America after Atlantis's fall they were supposedly shaped into skulls as a mix of Atlantian and Olmec cultures.
Regardless of which of these outlandish origins they believe, many believe in the supernatural abilities of these crystal skulls. Joshua Shapiro is a notable advocate of the powers the skulls supposedly possess. In his book, Mysteries of the Crystal Skulls Revealed he suggests that the skulls possess healing abilities as well as having the power to expand psychic abilities. Furthermore, he believes them to be a sort of super computer that can record energies and vibrations around them. The skulls are then able to create images to replay from these vibrations that act as a sort of visual history of the world. Some see the skulls as sentient deities. Many of what are sometimes called "skull enthusiasts have developed a whole mythology about the abilities and sources of the crystal skulls. This formation of a mythology can be explained by the concept of interpretive drift. Interpretive drift is a concept that can be used to explain how otherwise average people can develop alternative viewpoints through changes in rationalization, interpretation, and experience that can develop due to beliefs and practices. The concept would explain how skull enthusiasts become so set in their beliefs that outsiders could not influence them even with empirical data. 
Some of these crystal skulls are still on display in museums as genuine artifacts. In Mexico's national museum there are several crystal skulls that are presented as real, genuine Aztec works despite their lack of archaeological evidence. The British Museum has its skull on display as well but it is labeled as a fake.
In one study done on the skulls in the Musée du quai Branly collection in Paris, archaeologists analyzed the two skulls using optical microscopy, scanning electron microscopy (SEM), and Elastic Recoil Detection Analysis (ERDA). The optical and SEM imaging both suggested that the tool marks left on the crystal were made using machine lapidary techniques. These techniques would not have been available to the Aztecs. Furthermore, the hydrogen profiles of the skulls gathered through use of ERDA were compared to the hydrogen profiles of a reference quartz sample cut in 1740. The results indicate that the crystal skull was cut after the reference sample meaning that it must have been cut after 1740. Through the culmination of these methods the archaeologists were able to conclude that the artifacts were likely not pre-Columbian but rather likely to have been manufactured in the 18th or 19th century. 
In another study conducted on the British Museum's crystal skull as well as one recently donated to the Smithsonian, archaeologists once again utilized SEM to study the tool marks. This time the tool marks were compared to the tool marks present on a Mixtec rock crystal goblet and a group of Aztec/Mixtec rock crystal beads which were from known archaeological contexts. The crystal skulls once again show evidence of lapidary techniques, while the other contextually sound artifacts appear to have been shaped using stone and wood tools charged with abrasives. Both skulls were carved with rotary wheels which simply was not a tool that pre-Columbian Aztecs had. The British Museum's skull was worked with a hard substance like corundum or diamond, while the Smithsonian skull when analyzed using X-ray diffraction was revealed to have had been worked with carborundum, a hard modern synthetic abrasive. Moreover, using Raman spectroscopy on the British Museum's crystal skull revealed it was likely from Brazil or Madagascar, not Mexico. This article concludes that he British skull was likly made in the 19th century and the Smithsonian in the 1960's likely right before it was bought. 
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Mesa, Jose. Londres enero 2012 35 British Museum. Cráneo de cristal. 2012, Photograph, Flicker.