Mesoamérica Foundation

More precious than metal, jade was highly prized by the Maya and most other Mesoamerican societies. George Harlow, a mineralogist, explores the origins of Mesoamerican jade in “Hard Rock.”

Hard Rock

by George Harlow

A mineralogist explores the origins of Mesoamerican jade.

When the Spanish conquistadors entered the territory of the declining Maya civilization in search of gold, they overlooked what the Maya considered a more valuable resource, their jade mines. Along with the Aztecs and other Mesoamerican groups inhabiting Mexico and Central America, the Maya were avid users of jade, sculpting and polishing the rare, hard, usually green rock into ornaments, figurines, and other treasured objects. But the material was new to the sixteenth-century Europeans, who had yet to appreciate the riches of Asian jade. In some cases they excitedly mistook jade artifacts for emeralds.

Jade was prized by Mesoamericans as far back as 3,500 years ago. Prominent among the earliest craftsmen were the ancient Olmec of southern Veracruz and Tabasco, Mexico, who were unequaled at cutting and polishing jade rocks. Judging by the quantity and quality of their artifacts made of blue-green rock, the Olmec apparently preferred that color over others. Maya jade artifacts, many of which have been unearthed at important sites and graves of the Classic period (roughly A.D. 250 to 900), are more often a mottled green and white, while their choice pieces were of an emerald green variety.

The term jade is a fuzzy one, embracing a range of different rocks, the most important of which are jadeite rock, or jadeitite, and nephrite. Of the two, jadeitite is the only one found in Mesoamerica and considered by lapidaries and connoisseurs to be the finest jade from Asia. It is composed principally of the mineral jadeite, a sodium aluminum silicate. In pure form this mineral is white, but substitution of iron (and less commonly, chromium) for a tiny fraction of the aluminum yields a green coloring. Jadeitite is tough (it is difficult to break and doesn't fall apart) and dense (heavy for its size).

Nephrite is found in many parts of the world -- notably Turkistan, Siberia, Poland, New Zealand, and British Columbia -- but not in Mesoamerica. (Ironically, the term nephrite derives from the Latin lapis nephriticus, coined by Europeans to apply to Mesoamerican jade. The Latin name meant "kidney stone" and originated because some Indians wore jade amulets in the belief that the stone could cure kidney disorders.) Nephrite is not quite as dense as jadeitite but is the toughest known rock consisting principally of felted, intergrown, fiberlike crystals of the minerals tremolite and actinolite. These minerals are calcium magnesium silicates with variable amounts of iron substituting for some of the magnesium, again producing a green color.

A further complication is that the term jade is often applied to other green rocks that the Maya and their neighbors sculpted, some of which are formed in close association with jadeitite but none of which has the same mineralogy or chemical composition. These include serpentine, certain quartz rocks (notably chrysoprase and fuchsite jasper), and green albitite (albite rock, a transformation of jadeitite). In using the term jade, I will be referring strictly to jadeitite.

Knowledge of the source or sources of Mesoamerican jade was lost following the upheavals of the European conquest and remained a mystery as late as the 1950s. Since jade artifacts are distributed widely in Mexico, Central America, and the Caribbean, for a century or more people have searched for sources over a large area, even speculating that the raw material originated in Asia. Finally, in 1952 a sample rock found near the small town of Manzanal, Guatemala, in the central valley of the Rio Motagua, was identified as jade. Further investigation revealed a nine-mile-long zone on the north side of the valley, paralleling the highway leading to the Atlantic coast, that was mined for jade in prehistoric times and can still yield commercially useful amounts.

Following rediscovery of the Motagua Valley source, archaeologists have tried to determine whether or not it was the sole origin of jade for all the scattered Mesoamerican artifacts. For example, archaeologist Ron L. Bishop and his associates Edward Sayer and Lambertus van Zelst examined more than 300 jade artifacts using a technique called instrumental neutron activation analysis, in which samples are bombarded with neutrons and the resultant radioactivity is measured. (The technique has the advantage of not harming artifacts, but the objects remain radioactive for several months and so must be kept isolated.)

Using this technique, Bishop and his colleagues measured the proportions of ten different elements in each of their artifacts and reported in 1983 that about half the samples did not chemically resemble raw jade they had collected from the Motagua Valley. Most of the unmatched pieces felt into three categories. There were two varieties of emerald green artifacts -- what they called "Chichén green" beads from the sacrificial well at Chichén Itzá and "chrome green" pieces from all over the Maya area. In addition, there were blue-green celts and other objects from Costa Rica (blue-green Olmec material was not tested but probably could be grouped with the Costa Rican samples). As a result, Bishop and his colleagues concluded that several sources for Mesoamerican jade remain to be found.

Having an interest in the mineralogy and geological origin of jade, I tried to throw some new light on this question. Laboratory experiments have shown that jadeite, the principal component of jade, is formed under a combination of conditions that is unusual in the earth's crust: high pressure (as encountered at depths of at least fifteen miles) and relatively low temperature (400 to 700 degrees Fahrenheit, as compared with a more typical 1300 to 1500 degrees for such depths). Such conditions occur naturally when plate tectonic collisions push slabs of cold crust relatively rapidly down beneath an adjacent piece of crust, the "diving" plate reaching the fifteen-mile depth in only one or two million years. Jadeite is readily formed under such conditions; the catch is that it rarely makes it back to the surface without in the meantime encountering other conditions (higher temperatures being the most perilous) that transform into other minerals.

In addition, while a variety of rocks contain small amounts of jadeite, to qualify as jade, a sample must contain at least 90 percent jadeite. Jade is very rare, and only a handful of sources are known apart from the Motagua Valley, including localities in northern Burma, Japan, northwestern and south-central Russia, and western California. When found in place, jade always turns up as masses or veins within serpentinite, a green rock named for its undulating, layered texture. At some point, serpentine apparently plays a role in concentrating jadeite into jade. Veins of jade range from a few feet to a hundred feet across, but individual solid blocks of jade rarely reach ten or twelve feet in diameter.

Most serpentine does not contain jade, however. Generally, one has to look for serpentine near a large side-slipping fault, like the San Andreas fault. Such faults seem to provide, first, a conduit for watery fluids in the serpentinite to concentrate jadeite into jade and, second, relatively speedy pathway to bring jade safely to the surface. A further consideration is that wherever uplift occurs rapidly, so does erosion, which eventually destroys the jade brought to the surface. So one must look in fairly young terrain (less than 100 million years old). Finally, jade is also found with other unusual rocks, further indicators of the special geological conditions. Based on all these clues, we can anticipate regions in Mesoamerica where jade might be found.

The Motagua Valley follows the Motagua fault, an active fault that appears to be continuous with the Swan Fracture Zone, which cuts the floor of the Caribbean Sea and is the boundary between the North American and Caribbean plates of the earth's crust. The Motagua fault is the major fault of the right kind in the Mesoamerican region, although there are other related faults in Guatemala. Serpentine is found along portions of these other faults, but neither jade nor any of the unusual rocks associated with it appear to be present.

One might expect to find jade in Cuba or Hispaniola, which are located along the Swan Fracture Zone and other parallel faults. In fact, rocks containing grains of jadeite have recently been described from the Dominican Republic (in Hispaniola), but so far none are jadeite-like. The only other significant faults in this part of the world that have side-slipping motion are in Venezuela and Colombia. Again, jade-bearing rocks have been found in Venezuela, but no jade. Southern Mexico and northwestern Costa Rica also have some sources of serpentine, but these are not connected with major side-slipping faults and have yielded no jadeite-bearing rocks or typically associated unusual rocks.

So far, then, the Motagua Valley remains the only apparent source in the region. If so, where might the emerald green and blue-green jades have come from? To answer this question, I have collected hundreds of pounds of additional raw samples in the Motagua Valley and analyzed about twenty-five Mesoamerican jade artifacts in great detail. In 1984 a student and I surveyed the serpentinites in a twenty-five-mile section of the north side of the central Motagua Valley, particularly where cross-cutting streams would expose the tougher jade. We found some rocks near La Palmilla, about six miles east of Manzanal, that resemble some of the emerald green materials. (Although we did not find any blue-green rocks, more recently, a new productive site along the Motagua Valley has been reported by the owners of a jade workshop, who are keeping the exact whereabouts secret. I have not fully analyzed this new material, but some of it looks similar to the darker blue-green artifacts from Costa Rica.)

To study Mesoamerican jade artifacts and rock samples, I chose a technique called electron microprobe analysis. The electron microprobe is a specialized electron microscope that can determine the composition of even a small speck of a mineral lying in a polished surface. It can be safely used on artifacts, provided they are small enough to fit into the instrument (no more than about five inches in diameter and two inches thick.)

Unlike instrumental neutron activation analysis, the electron microprobe provides a look at the individual minerals making up a rock, not just the bulk composition. Although mostly jadeite, jade is not a homogeneous substance but an assemblage, or aggregate, of several minerals, each with its own range of chemical composition. In addition to yielding insight into the geology of jade formation, the detailed mineralogical information obtained with the electron microprobe provides a better means to distinguish jades originating from different deposits.

Under the scrutiny of the electron microprobe, one can sort most jade among the various known geological sources in the world. The key minerals for jade from the primary Motagua Valley source are jadeite, omphacite, albite, white mica (two varieties), and titanite. The jade and many other rocks found with it contain some or all of these minerals in various amounts, as well as several other minerals that are less distinctive but still useful clues to their origin. In examining Mesoamerican artifacts, I found that both the assortment of minerals they contain and their chemical compositions show a resemblance to Motagua rock samples; they could not, for example, be confused with Burmese jade.

I knew that jadeite in which as little as one percent of the aluminum atoms are replaced by chromium is a very strong emerald green. Chromian jadeite rock, called imperial jade, is well known from Burma. Analysis of emerald green Mesoamerican artifacts of the type Bishop and his colleagues classified as “chrome green,” however, showed all but one to be composed principally of chromian omphacite, a mineral that is roughly half jadeite and half diopside (a calcium magnesium silicate). Strictly speaking, therefore, these pieces -- as well as the new, similar samples of rock I found in the Motagua Valley -- were not jade.

The exception was an emerald green bead from an Olmec site that proved to be mostly jadeite and white mica with small areas of chromian jadeite and other related minerals. This is the "Chichén green" kind of emerald green. Although it only slightly resembles one rock sample found in Guatemala, the association of jadeite and white mica and other minerals is completely consistent with Motagua Valley rock.

Blue-green jade artifacts contain slightly iron-enriched jadeite, a fair amount of titanite, and albite, all typical for the range of minerals found in the Guatemalan rocks. Although even the newly discovered Motagua Valley source does not seem to match the ancient examples exactly for color and mineralogy, there are no major surprises. The bottom line is that all the Mesoamerican jade artifacts examined so far are consistent with Motagua Valley sources, although perhaps more than the two specific areas now known there.

A single regional source for jade means that extensive transport accounts for the wide distribution of these artifacts. Archaeology offers few clues to the social arrangements by which this was accomplished. Among the things to be explained are the predominance of blue-green jades among Olmec and Costa Rican artifacts, and of Chichén green at the sacrificial well at Chichén Itzá. Did each culture operate its own quarry for hundreds of years to get its special variety (suggesting they would have had to defend their particular source) or did some local entrepreneurial extractors supply the needs of the various cultures through trade?

The valley is not the most hospitable environment, so that in the past, as in the present, the major centers of actual stoneworking may have been elsewhere, such as in the Guatemalan highlands. The only site of any size is Guaytan Castillo, about six miles west of the main known jade source. The nearest significant cities, Kaminaljuyu, in the highlands, and Copán, across the present border with Honduras, are neither close nor well situated to control access. If expeditions were made to the valley from outside, however, no long-term residence and access controls may have been required. Conceivably, the valley was treated as a sacred source, unoccupied and undefended, to which various peoples made pilgrimages to retrieve stone for back home.

Contrasted with the paucity now found in the field, the large quantity of the emerald green “jade” (chromian omphacite) and artifacts suggests that the source has been much depleted or that in their quest ancient peoples searched the valley much more intently. Probably both hypotheses are true. At every jade prospect, flaked obsidian from imported stone tools is found in the mounds of jade rubble. The Maya and others must have developed a keen eye for green rocks and literally left no stone unturned.

George Harlow is Chairman and Curator of the Department of Mineral Sciences at the American Museum of Natural History, New York.

“Hard Rock” was originally appeared in Natural History's series.  “The Maya Rediscovered.” We wish to thank author George Harlow and editor Carol Burnett for their generous cooperation; a Spanish translation of this article is now available from Mesoamerica Foundation.