Opinion, Berkeley Blogs

"Liquid mercury found under Mexican pyramid"...

By Rosemary Joyce


That's the beginning of the headline on an article in Britain's The Guardian published on April 24. Alan Yuhas, the reporter from The Guardian , has done a super job in this report of balancing comments from specialists with an attempt to convey what is exciting here.

Since I ended up quoted rather a lot (considering that I was talking on a cell phone while at a café for breakfast, without notes, and mainly trying to think who I could suggest to provide expert information), I was motivated to follow up on my off-the-cuff summary of previous finds of liquid mercury in prehispanic sites in Central America with something a little more precise.

I should begin with one correction: liquid mercury hasn't been reported from any Olmec sites, so far as I know. In research published in Science in 1975, archaeoastronomer John Carlson demonstrated that a hematite object excavated at the Olmec site of San Lorenzo, in the Gulf Coast of Mexico, could act as a compass oriented to magnetic north if it was floated on liquid mercury. Carlson specifically suggested that the Olmec might have used liquid mercury in this way. That report was picked up by others and recently, even scholarly works have stated as a fact that liquid mercury was used starting around 1000 BC.


The red powdery form of mercuric sulphide, cinnabar, was definitely used by early Mesoamerican people, among other things, covering carved jade and ceramics. Pieces of cinnabar have been reported from the Highland Mexican site Chalcatzingo, dating before 900 BC, when a burial at the site contained a green serpentine figure so thoroughly covered with cinnabar that it looks red.

But it is in sites dating much later that archaeologists have found liquid mercury itself.

The majority of the reported finds come from the highlands of eastern Guatemala and western Honduras -- areas where cinnabar is found naturally. At Lake Amatitlan , Kaminaljuyu , and Quirigua in Guatemala, and from Copan and El Paraiso in western Honduras, liquid mercury was recovered, always in special deposits suggesting its symbolic importance.

The reported context of liquid mercury at Kaminaljuyu was in tombs; at Lake Amatitlan, in vessels deposited in the waters of the lake as steps in rituals.

One of the instances of liquid mercury at Quirigua came from a cache associated with carved stone Monument 21 . This deposit was burned in place, and the excavator, Professor Wendy Ashmore of UC Riverside, argued that the burning of cinnabar produced the liquid mercury found here.

An equally striking find of liquid mercury was a cache under the central ballcourt marker at Lamanai, Belize. A cache excavated at Caracol, Belize, reportedly contained a large quantity of mercury as well.

Many, perhaps all, of the liquid mercury deposits in Maya sites date to the earlier part of the Late Classic period (before 700 AD). This generally overlaps with the period when Teotihuacan, in central Mexico, reached its greatest size and wide influence. But the deposits being explored by the current Teotihuacan project under the Temple of the Feathered Serpent predate 400 AD, when its lavishly decorated facade was covered over.

Sergio Gomez, the lead archaeologist on the team slowly excavating the contents of the ancient tunnel below the pyramid, has suggested that the tunnel might have been sealed off as early as 200-250 AD. That would make the presence of liquid mercury substantially earlier at Teotihuacan than in the group of Maya highland sites where it has been repeatedly recovered. One cache, from Caracol, has similarly early dates.

A major point of disagreement among archaeologists writing about finds of liquid mercury has been whether it was collected from naturally occurring deposits, or produced by processing cinnabar, as Ashmore argued for Quirigua. David Pendergast, excavator of the ballcourt cache at Lamanai, described the large quantity of liquid mercury there as likely collected in the highland area of Honduras or Guatemala, where naturally occurring deposits of native (liquid) mercury could potentially be found accompanying cinnabar.

USGS reports from the 1950s do describe some native mercury in Honduran cinnabar deposits near the capital city of Tegucigalpa, and some of these were exploited by Spanish colonial miners who used mercury in processing silver ore. However, this area is far beyond the zone where exchange was established with Maya sites in Belize. Large cinnabar deposits are known from the Honduran Department of Santa Barbara, within the zone of known interaction with the Maya sites of Belize, but there are no reported incidences of native mercury in these deposits -- although they could exist.

Still, collecting tiny amounts of native mercury seems like a greater challenge than burning cinnabar ore.

The archaeological record from Mexico provides grounds to suspect prehispanic peoples did process cinnabar to produce mercury. Native mercury is present in northern Mexico (the States of Durango, Guanajuato, Guerrero, San Luis Potosi, and Zacatecas), in association with cinnabar deposits.

In 2011, two Mexican specialists in archaeological chemistry, Luis Barba and Alberto Herrera, published an article describing evidence for mercury production from cinnabar at San José Ixtapa, an archaeological site in the northern state of Queretaro. The site is described as dating to 1100-1200 AD, after Teotihuacan was abandoned. Specific types of pots recovered at the site were shown to be used during this period to produce mercury from cinnabar.

While San José Ixtapa itself was occupied later than Teotihuacan, and Maya sites like Quirigua, and Lamanai, there is no reason to assume the technology was invented at that late period. Rather, what this site does is open a window that allows us to see a technique that allowed processing of a potentially poisonous material prized for its red color to produce a silvery liquid that was among the rarest minerals used by indigenous peoples of the Americas.

With the new discovery at Teotihuacan, we can now say with certainty that mercury was used in ritual before 400 AD in Mexico. The technology required to produce mercury from cinnabar was entirely within the reach of people in this area as soon as they were able to fire pottery (long before 1000 BC).

It is still possible that people collected liquid mercury where it was found in small quantities along with cinnabar. But the amounts in deposits at several sites were large. The cache at Quirigua contained both unconverted cinnabar and mercury, and had clearly been burned. Burning ritual objects was a practice with deep cultural roots in the area, and if applied to quantities of cinnabar, would have promoted the creation of liquid mercury.

And that entire process, transforming a solid, red powder into a silvery liquid, through the application of ritual fire, might well have been part of what made this substance a particularly important material for ritual deposits.