Last updateSat, 22 Jun 2019 1pm

Archaeologists complete first excavation of an obsidian mine and workshop in Jalisco

Jalisco has the fourth-largest obsidian deposits in the world but until now no excavations have ever been carried out to study in detail the process by which a chunk of this volcanic glass was transformed into useful artifacts by pre-Hispanic people.

pg8aAs I reported in this column on May 10, a location deep inside Ahuisculco’s Selva Negra Nature Preserve was chosen for the dig because it represented all the stages of production from mining to completion of much-prized, dual-color (meca) bifacial blades.

“On top of that,” archaeologist Rodrigo Esparza explained to me, “this part of the Ahuisculco Forest appears to have been relatively undisturbed for perhaps 2,000 years.”

The excavation was carried out by digging three, one-meter-square holes, removing everything in them layer by layer and examining and sorting every item found. The result was more than 1,000 kilos of what most of us would consider rubble.

“It’s not rubble to us,” archaeologist Camilo Mireles told a group of 11 volunteer sherpas – including myself – who had come to give him a hand.

“A ton of rocks is too much for us to transport to our lab in Michoacán,” Mireles continued. “So we have picked out 300 kilos of samples for technicians to examine one by one and fit each item where it belongs in the production sequence.”

Mireles explained that there were no precedents for this sort of dig, so his team had no references telling them what to expect or what methodology to use. “We devised a plan of attack, came out here and tried it, went back and revised the plan ... and finally we are delighted with the results. And soon we will see how all the pieces fit together.”


Mireles said some of the samples will be sent for chemical analysis to determine the components of this particular obsidian. “This will help us a lot because we plan to go to museumsand private collections which have knives like these, to see whether those artifacts came from here in Selva Negra or someplace els

As to the age of workshop, Mireles was cautious.  “We haven’t found anything containing carbon so far but we hope to find the answer using Obsidian Hydration Dating, or OHD,” he said.

Obsidian typically contains less than one percent water, but once a fresh obsidian surface is exposed to the elements, it begins to absorb water at a well-defined rate. After a while, what appears to the eye is a sort of white patina whose thickness can be measured, giving an idea of how long that item was lying on the surface since the day it had been worked and then cast aside – probably because it broke or did not meet the quality standards of the craftsman. For OHD to result in accurate dating, a great deal of information must be gathered about local conditions, especially weather processes.


Obsidian is known to contain up to 59 trace elements such as zinc and gallium as well as rare elements like molybdenum.Modern-day techniques can determine their presence with great accuracy, producing a “fingerprint” matching a certain artifact with a certain deposit. 

pg8dThe technique has already proven, for example, that some tools found in Arizona and used by the Anasazis, could only have come from Jalisco. Archaeologists hope that they will ultimately find well-dated items from the Encinar deposit in some museum or private collection. For the moment, they are guessing that obsidian mining and manufacturing was carried out in the Ahuisculco Forest over some 800 years during the heyday of the Teuchitlan Tradition around 2,000 years ago.

I was one of the “sherpas” who helped the Selva Negra team carry 300 kilos of obsidian along a kilometer-long trail from the Project Encinar excavation to waiting trucks. The archaeologists remained behind to refill their holes (in reverse order) with material they don’t plan to use. But first they placed, at the bottom of one hole, a Coca Cola bottle with a note telling future archaeologists “what we did here.”

Encinar was financed by the Jalisco Secretariat of Culture’s Proyecta Fund which supports projects that promote economic and cultural development in the state. The archaeologists would like the Encinar site to remain undisturbed, but don’t worry, there are dozens of similar obsidian workshops and mines at Selva Negra and there’s even a special trail laid out to guide you to them. If you have a high-clearance vehicle, you can visit this forest by following the route “Ahuisculco to Selva Negra Woods” on Wikiloc.com.  Driving time to the parking spot is about 90 minutes from either Guadalajara or Ajijic.

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