Re-Discovery of Olmec Blue Jade

Shortly after the Spanish conquistadors first interacted with the Aztec culture, they were given four samples of raw green jade. An Aztec emissary told Cortés that these stones were the most precious items in the entire Aztec treasury and should be sent directly to the Spanish King Charles V. However, the Spanish lusted after gold and not stones; this caused the demand for jade to cease. There was an approximately 400-year interval in which the source of Mesoamerican jade was not known. In the 1950s, a Guatemalan tomato farmer led William Foshag to a site in the Motagua river valley and showed him green jade similar to that commonly used in Aztec and Maya cultures. However, the source of the blue-green jade used by the Olmec (a Mesoamerican formative culture) remained a mystery until recent work by a group of geologists and archeologists, as reported in the New York Times and Houston Chronicle on April 22, 2002.
Jade is a common name for a rock almost entirely made of either nephrite (a type of amphibole) or jadeite (a sodium-rich pyroxene). Nephrite jade is more common and was used extensively in early Chinese jewelry and sculpture. Jadeite jade (or jadeitite) is much more rare as it only occurs in 8 to 10 localities around the world with prime commercial jadeitite produced in northern Myanmar (formerly Burma). It typically is hosted in serpentinite as either veins or tectonic blocks. Jadeitite precipitates from seawater in subduction zones (Johnson and Harlow, 1999). Jadeitites typically occur with other high-pressure, low-temperature rocks such as eclogites (a garnet pyroxene rock) and blueschists (predominantly a glaucophane-bearing rock). Often jadeitite occurrences are associated with strike-slip fault zones. The processes that form jade are still being deciphered to understand how it is exhumed back to the Earth’s surface and what causes the extensive range of colors including white, black, mauve, lilac and numerous shades of green including the blue-green found only in Olmec artifacts.
Geologists and archeologists seeking jadeitite concentrated their exploration in the northern Motagua River valley where there are abundant outcrops of serpentinite (e.g., Harlow, 1994). This valley is the trace of the Motagua fault, a left-lateral, strike-slip fault that has up to 1,200 kilometers of offset and separates the North American plate from the Caribbean plate. Previous studies and commercial exploration only found jadeitite as either alluvium or as dismembered tectonic blocks hosted by serpentinite. Substantial erosion partly associated with Hurricane Mitch in 1998 revealed blue-green jadeitite boulders and serpentinite outcrops 10 kilometers south of the Motagua valley. Local farmers began collecting the material, but the Guatemalan jade market preferred green material for creating jewelry and replicas of Mayan artifacts, so, Montagua Valley jadeitite was not used in commercial pieces. Russell Seitz found an unused piece in a jade shop in Antigua, Guatemala and was subsequently shown the location for this jade. He contacted Dr. George Harlow of the American Museum of Natural History to confirm this was indeed jadeitite. He then invited Harlow, Dr. Karl Taube, an archeologist from University of California at Riverside, and myself to see the locality. In March 2001, we spent 10 days looking at various sites to confirm ancient jade workings as well as the geologic setting of the jadeitite. We were also taken to a site in the Sierra de las Minas Mountains well north of the Motagua fault zone. There was a dry stone trackway that led directly to the jadeitite locality. It is not known how old this trackway is and whether it has any relation with ancient cultures. Future archeological studies will hopefully determine this and whether or not Olmec or Mayan cultures took material from this site for jade working. While we were there, we were told that jadeitite was being found south of the Motagua valley. Another trip occurred in June to verify this fact. The results of these two trips are discussed in Seitz et al. (2001).
Subsequent to our discovery, we found that Richard Mandell, a retired sports historian, also found pieces that are similar to Olmec blue jade during his interactions with farmers in Guatemala in 1999. Also, a local jade entrepreneur and archeologist, Mary Lou Ridinger, found pieces in 1987 that may be similar to Olmec blue jade. None of these findings, however, was reported in either geologic or archeological publications.
In addition to jadeitite, the serpentinite hosts other high-pressure metamorphic tectonic blocks. To the south of the Motagua fault, these blocks are typically eclogites and blueschists. In contrast, the tectonic blocks in serpentinite north of the Motagua fault are garnet-amphibolite rocks that form by retrogression of eclogite. This implies that the two sides of the fault have different subduction histories. We do not know if this is caused by a change in plate tectonic setting with time or whether these different blocks just represent different events in one relict subduction zone. In addition, there are albitites (rocks composed mostly of albite feldspar with some white micas) on both sides of the Motagua fault. These are presumed to form in a similar manner to jadeitite but at lower pressures and temperatures in the relict subduction zone. Thus, the rock suites hosted in the serpentinite give us a sampling of many different levels from exhumed subduction zone(s).
Plans are now being made for future geologic studies to constrain the pressure-temperature for formation of jadeitite, eclogite, and blueschist formation (both north and south of the Motagua fault); geochronology of jadeitite formation; and accessory minerals in the jadeitite from north and south of the fault. The latter study will help relate the jadeitite in outcrop to various artifacts. We hypothesize that the accessory minerals vary between different outcrops and thus can be used to “fingerprint” the jade in artifacts. Dr. Hans Avé Lallemant of Rice University will also study these jadeitites and their host serpentinite to determine how they were exhumed back to the surface from the relict subduction zone. Archeological studies will try to determine when the material was mined at various locations by the different Mesoamerican cultures.
Biographical Sketch
Virginia Sisson is a Research Scientist in the Department of Earth Science at Rice University. She earned a BA in geology at Bryn Mawr College, and both an MS and PhD at Princeton University in metamorphic petrology. Her focus continues to be on metamorphism and tectonics. For over 15 years, she has worked in southern Alaska doing fieldwork, geochronology, geochemistry and petrology on the accretionary margin looking at the effects of Paleogene ridge subduction. She also has done similar studies in northern Venezuela with Dr. Hans Avé Lallemant on determining the maximum depth of burial and exhumation of two subduction related compexes. This research led to the current studies on jade beginning with a field excursion to Myanmar (formerly Burma) two years ago.
References cited:
Harlow, G. E. (1994) Jadeitites, albitites and related rocks from the Motagua Fault Zone, Guatemala. Journal of Metamorphic Geology, v. 12, p. 49-68.
Johnson, C. A., and Harlow, G. E. (1999) Guatemala jadeites and albitites were formed by deuterium-rich serpentinizing fluids deep within a subduction zone. Geology, v. 27, p. 629-632.
Seitz, R., Harlow, G. E., Sisson, V. B., and Taube, K. E. (2001) Formative jades and expanded jade sources in Guatemala. Antiquity, v. 75, no. 290, p. 687-688.
Guatemalan field party guide, Carlos Gonzales, by a big boulder of jade that was uncovered in Hurricane Mitch.
Figures:
Figure One: Guatemalan fi