2. Methodology

The first step of this study was the characterisation of the archaeological artefacts made of greenstone. The ancient systematic use of serpentinite (antigorite: ((Mg, Fe)3Si2O5(OH)4)) and gneiss for the manufacture of different kinds of artefacts was characterised with the aid of petrography and XRD.

In order to ensure a representative sample, we took examples from different stages of production or different types of artefact, as well as from different sites with a range of administrative hierarchies (i.e. regional centre, satellite sites, etc.); and also, we took examples from archaeological sites of the Olmec culture with different dating in order to see how the quarries changed through time.

After we had characterised the Olmec archaeological objects, we then narrowed the options of the provenance of the rocks. We focused on the quarries with the same petrographic characteristics. We also took into consideration:

archaeological evidence of Formative archaeological remains
cultural continuity in the use of the quarries during Pre-hispanic times
the existence of ethnohistorical accounts about the use of the quarries
contemporary use of the quarries by the local ethnic groups

Figure 2: Quarries of serpentinite (antigorite) in Cuicatlán Oaxaca
Figure 3: XRD from a sample of serpentinite from Cuicatlán Oaxaca

We sampled the quarries that we had chosen. We decided to sample Tehuitzingo (Puebla, México) and Cuicatlán (Oaxaca, Mexico). Cuicatlán is the biggest quarry of serpentinite (antigorite) in Mesoamerica (Figs 2, 3, 4 and 5). It has Pre-hispanic occupation and the ethnic groups who live there still use this rock in their everyday life. Cuicatlán was connected with the Gulf Coast by a series of rivers.

Figure 5: Micro-photograph of a thin-section of a sample from Cuicatlán, Oaxaca

In regard to Tehuitzingo, this quarry has Formative occupation, evidence of manufacture of serpentinite, and the Aztec (Post-Classic) glyph and place-name means 'place of rock manufacture'. Both quarries are located in the Highlands of Mexico, far away from the Olmec tropical lowlands (Figs 6, 7, 8 and 9).

Figure 6: A sample of serpentinite from Tehuitzingo, Puebla
Figure 7: Micro-photograph of a sample of serpentinite from Tehuitzingo, Puebla

Figure 8: XRD difractogram of a sample of serpentinite from Tehuitzingo, Puebla

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