A Diffraction Signal in the pXRF Data

In the pXRF spectra of the Light irradiation stage (Figure 11) for the chemical signatures of the serpentine sampled from the Tehuitzingo, Puebla, deposit, we encountered a signal located at 4.47 keV (Figure 12), which cannot be assigned to any radiation characteristic of XRF or distinct satellite lines. Curiously, the shape of this peak differs significantly from the usual form present in lines characteristic of XRF, while it coincides with the perfect Gaussian form described for diffraction signals (Alfonso et al. Reference Alfonso, Lavelle, Greaves and Sajó-Bohus2002). We thus infer that this is, in fact, a diffraction signal. Notably, this signal is not evident in the serpentine from Río Verde, Oaxaca. The peak between 4.3 and 4.75 KeV in Figure 12 corresponds to the XRF identification of Ti in the Oaxaca sample. This fact, in turn, indicates that the signal derives from a crystalline structure and not from chemical composition, since its presence in the spectrum is conditioned by the orientation of the cut made for the separation of the piece that constitutes our sample.

Figure 12.

Portable dispersive energy X-ray fluorescence spectrometry spectra corresponding to the Light stage of irradiation of the chemical signatures of the serpentine samples (SP1 and SP2, Puebla serpentine; SO, Oaxaca serpentine), in which the presence of an X-ray diffraction (XRD) signal is noted at 4.47 KeV in the Puebla serpentine spectra.

The presence of diffraction signals in fluorescence spectra is not entirely unusual, and has been reported in the scientific literature (e.g., Mendoza Cuevas and Pérez Gravie Reference Mendoza Cuevas and Gravie2011). These authors report that, theoretically, the relationship between the energy at which the signal appears and the interplanar distance it represents may be calculated according to following equation:

$${\rm E}\;{\rm d}\; {\rm sen\theta } = 6.19926\; {\rm keV} {\rm {\Aring}}$$

This equation applies only to cases in which both the angle of incidence of the primary radiation (θ₁) and the angle of output of the radiation detected (θ₂) are equal. In the geometric conditions of analysis associated with the portable spectrometer employed in this study, however, these values are distinct: θ₁ = 71°; θ₂ = 61° (Steyn Reference Steyn2014:17; Thermo Fisher Scientific 2011). Thus, we developed the following equation to determine interplanar distance:

$${\rm E}\; {\rm d} \lpar {{\rm sen}{\rm \theta }_1 + {\rm sen}{\rm \theta }_2} \rpar = 12.39852\; {\rm keV} {\rm {\Aring}}$$

This results in a calculated interplanar distance of 1.52 Å. Various studies (e.g., Bailey Reference Bailey1969; Esteves Reference Esteves Teixeira2016:132; Fryer and Mottl Reference Fryer, Mottl, Fryer, Coleman, Pearce and Stokking1992) report this interplanar distance as an identifying characteristic of serpentine.

This interplanar distance is not, however, one of the fundamental characterization signals of serpentine, which are 7.3 Å, 3.64 Å, and 2.52 Å (Valdivia et al. Reference Valdivia García, Arostegui, Alonso Pérez, Cabrera, Hernández, Herrera, Cruz, Casanova, Martínez, Díaz and Aguila2014). These distances are identifiable in XRF spectrums in energy signals at 0.93, 1.87, and 2.7 keV, respectively. In this case, however, such XRD peaks are not observable via XRF, since they occur in a low-energy range. Such low ranges present analytic difficulties for the spectrometer we employed, and the XRD peaks would therefore overlap XRF signals, such as occurs at the distance of 2.57 Å, which encounters interference with the Kɑ peak of Cl.Nonetheless, the interplanar distance we calculated does provide an additional data point for the identification of the CB mineral matrix and its source.

If the CB is, in fact, Tehuitzingo serpentine, then we should expect to encounter the diffraction signal described above—and noted in the samples—in the pXRF spectra of the object. In the Light irradiation stage spectra (Figure 13), just such a signal is detected at 4.47 keV, associated with the interplanar distance of 1.52 Å. This is identical to the peak observed in the spectra of the Tehuitzingo serpentine (SP1 and SP2 in Figure 12), but not in the Oaxaca serpentine (SPO in Figure 12) or additional greenstone samples (Q and J in Figure 13). In conjunction with the qualitative pXRF data discussed above, this diffractometric spectral identification provides further data to establish definitively that the constituent material of the CB is serpentine, and supports the hypothesis that its source is the Tehuitzingo deposit in Puebla.

Figure 13.

Portable dispersive energy X-ray fluorescence spectrometry spectra corresponding to the Light stage of irradiation of the chemical signatures of the Cascajal Block (CB) and additional greenstone samples (J, jadeite; Q, green quartz), in which the presence of an X-ray diffraction (XRD) signal is noted at 4.47 KeV in the CB spectrum.

Patination Patterns and Contextual Information Revealed in the pXRF Data

A second set of anomalous readings appeared in the Light stage pXRF spectra. In these, potentially significant differences between the peak intensities of the Si and Mg signals are evident in the CB spectrum with respect to those of the serpentine reference samples (Figure 14). Due to the low Si and Mg readings for the CB matrix revealed in the pXRF spectra, we turned to the results of the quantitative chemical analysis (Table 1) to determine the mass concentrations of those elements present on the CB. Focusing for the moment on Si, the quantitative data show that, in terms of the interaction volume (in which the primary X-ray beam is completely attenuated), Si is found in mass concentrations between 1.26 ppm and 1.72 ppm. These values are somewhat unusual for the chemical composition of a lithic matrix, but may be attributable to the mineral qualities of serpentine. Since the Pearson Coefficient of Variation (CV) is less than 15 percent, we may conclude that the low concentration of Si on the surface of the CB is a generalized condition. Likewise, the unquantifiable fraction of the lithic matrix exceeds 90 percent, with a similarly low CV value (0.42 percent), which again suggests a generalized condition for the CB surface. Together, these data suggest the presence of a uniform patina on the CB surface, contrary to the variable patina apparently evident via visual examination and reported by Rodríguez Martínez et al. (Reference Rodríguez Martínez, Ceballos, Coe, Diehl, Houston, Taube and Calderón2006:1612).

Figure 14.

Portable dispersive energy X-ray fluorescence spectrometry spectra corresponding to the Light stage of irradiation of the chemical signatures of the Cascajal Block (CB) and serpentine samples (SP1 and SP2, Puebla serpentine; SO, Oaxaca serpentine).

Table 1.

Results of the quantitative chemical analysis of Cascajal Block (CB) surfaces. NQ, part of the matrix that could not be quantified; CV, Pearson Coefficient of Variation.

^a Sample areas were selected on the basis of visual inspection, to include both patinated and (apparently) unpatinated areas (although subsequent analysis indicated uniform patina).

^b See Online Appendix 1.

This patina could have formed through two geochemical processes. First, it is possible that the chemical-compositional characteristics are a consequence of the generalized presence on the CB surface of a mineral patina produced by authigenesis, a process whereby a mineral deposit (such as a patina) is generated where it is found or observed (Pérez Jiménez Reference Pérez Jiménez2010:238–242; Ritger et al. Reference Ritger, Carson and Suess1987; Ruttenberg and Berner Reference Ruttenberg and Berner1993), which would hinder the correct quantification of light chemical elements such as Si or Mg (due to the attenuation of the primary beam in the volume of the patina, which would cause considerable difficulties for the quantification of other chemical elements). If the patina was produced authigenetically, however, the CB would present a greater set of inconsistencies with the serpentine samples. But this is not the case. Rather, the mass concentrations of Fe, Cr, and Mn in the CB are consistent with the samples—evident in the Kɑ and Kβ signal intensities in the corresponding pXRF spectra (Figures 8–11), as well as in the quantitative data (Table 2). Comparing these data suggests Si and Mg are outliers in the CB spectra, since all other elemental determinations display strong similarities between the CB composition and the diagnostic chemical signatures of the (unpatinated) serpentine samples (% and ppm of Cr, Mn, and Fe in Table 2). As an aside, it is noteworthy that the quantitative chemical data in Table 2 also suggest stronger correspondences between the CB and the Tehuitzingo serpentine samples, and differences with the sample from Oaxaca (particularly in terms of Cr percentage), further supporting the identification of the Tehuitzingo deposit as the source of the CB serpentine.

Table 2.

Results of the quantitative chemical analysis of the Cascajal Block (CB) and the serpentine mineral samples. SP1 and SP2, Puebla serpentine; SO, Oaxaca serpentine; NQ, part of the matrix that could not be quantified.

It is more likely that these anomalous results are due to a patina produced via a superficial erosion process, through which the mass concentration of Si on all surfaces of the CB decreased significantly, to a level below two percent (Tables 1 and 2). A similar process may be surmised for Mg. In the case of serpentine, Krevor and Lackner (Reference Krevor and Lackner2011) have reported that these chemical characteristics—low levels of Si and Mg in mineral surface accumulations—are the result of the geochemical process of dissolution. In dissolution, hydrolysis of the surface crystalline structure occurs, with a consequent loss of SiO₂ and an accumulation of magnesium carbonate on the surface, via the following chemical reactions:

$$\eqalign{& ⅓{\rm M}{\rm g}_3{\rm S}{\rm i}_2{\rm O}_5\left( {{\rm OH}} \right)_4 \,+\, {\rm }2{\rm H}^ + \to {\rm }{\rm M}{\rm g}^{2 + } + {\rm }⅔{\rm Si}{\rm O}_2\left( {{\rm aq}} \right){\rm } + {\rm }⅔{\rm }{\rm H}_2{\rm O} \cr & {\rm M}{\rm g}^{2 + } + {\rm }{\rm HC}{\rm O}_3^- \to {\rm }{\rm MgC}{\rm O}_3\left( {\rm s} \right){\rm } + {\rm }{\rm H}^ + }$$

This process particularly affects serpentine in humid, acidic soils. Sanna et al. (Reference Sanna, Steel and Maroto-Valer2017) report that these reactions are accelerated in environments with high concentrations of sodium salts, which subsequently replace Si on the surface. The resulting accumulations of magnesium carbonate on the surface, however, tend to dissolve in these humid, saline contexts. In constant conditions, the process culminates with the establishment of a solid-liquid phase equilibrium after approximately six hours of contact (Dong et al. Reference Dong, Li, Mi and Demopoulos2009).

Of course, an archaeological context is a dynamic system in which conditions are rarely constant. In sealed contexts, a buried object will never be in contact with a constant volume of liquid, since soil humidity is dependent on variable hydrographic characteristics and levels of rainfall in a given region. Thus, in real-world conditions distinct from the ideals established by Dong et al. (Reference Dong, Li, Mi and Demopoulos2009), phase equilibrium is difficult to achieve, much less in a question of hours. Accordingly, dissolution of Si and (subsequently) magnesium carbonate and the consequent surface deposition of sodium salts is a long-term, continuous process, influenced by factors such as variability between the exchange rate and dissolution coefficient, ambient temperature, soil pH, and concentration of salts in the liquid phase (Dong et al. Reference Dong, Li, Mi and Demopoulos2009), particularly MgCl₂, since increased levels of this saline compound accelerate the dissolution of magnesium carbonate from the solid phase (Sanna et al. Reference Sanna, Steel and Maroto-Valer2017).

The simultaneous processes of dissolution of a serpentine matrix and dissolution of superficial magnesium carbonate may provide a window onto the depositional contexts and dating of a serpentine object that displays surface erosion and low levels of Mg. Konrad et al. (Reference Konrad-Schmolke, Halama, Wirth, Thomen, Klitscher, Morales, Schreiber and Wilke2018) report that the dissolution of serpentine takes between 10³ and 10⁵ years. We would thus expect that extended burial of a serpentine object in specific soil conditions would lead to surface erosion via dissolution. Dissolution, in turn, would result in the formation of a uniform patina that would display low mass concentrations of Si and Mg in spectrometric analyses, due to the continuous dissolution of the magnesium carbonate produced in the process of serpentine dissolution, which itself would be replaced by the deposition of sodium salts on the surface.

Our results reflect precisely such characteristics on the CB. The chemical determination of Mg in the CB matrix did not yield quantifiable results, whereas Mg is evident in the three other samples of serpentine (Tables 1 and 2). Further, the pXRF spectra corresponding to the Light stage of irradiation (Figure 14) also reflect this discrepancy and display significant differences between the intensities of the Kɑ signals of both Si and Mg for the CB relative to the serpentine samples. It is possible that uneven distribution of superficial sodium salts is responsible for what appears visually to be variable patina on the CB.

Since Mg is a fundamental element in the chemical composition of serpentine, its relatively low concentrations on the CB are most likely due to the specific edaphological characteristics of the context of its original deposition, which resulted in the dissolution process that yielded the specific chemical signatures of the object. The context reported for the discovery of the CB (Rodríguez Martínez and Ortiz Ceballos Reference Rodríguez Martínez and Ceballos1999, Reference Rodríguez Martínez and Ceballos2007; Rodríguez Martínez et al. Reference Rodríguez Martínez, Ceballos, Coe, Diehl, Houston, Taube and Calderón2006) is a riverine environment in which high humidity luvisols with an albic horizon predominate (INEGI 2019; López et al. Reference López Portillo, Martínez, Hesp, Hernández, Méndez, Vásquez-Reyes, Gómez Aguilar, Jiménez-Orocio and Gachuz Delgado2011:23). The average pH of these luvisols is slightly acidic, between 5 and 6 (Campos Cascaredo Reference Campos Cascaredo and Angón2011). Further, several salt domes are concentrated in the area (Benavides García Reference Benavides García1983), resulting in high levels of soil salinity. Thus, the soil conditions of the immediate area in which the CB was found are ideal for the geochemical process of dissolution to occur and produce precisely the chemical signatures evident in the CB spectra. The albic horizon reported for soils in the region is also significant in this regard, since it would cause a considerable deficit of Fe in the subsoil. Such conditions would impede excessive enrichment of the CB surface with this element, thereby explicating the similar peak intensities for Fe between the CB and the unpatinated serpentine samples.

The anomalous readings for Si and Mg revealed in the Light irradiation XRF analysis of the CB matrix thus have led, fortuitously, to three key inferences. First, these readings indicate the presence a generalized mineral condition on the CB surface, that is, a uniform patina. Although it is true that patina can be artificially induced, the presence of patination on the entirety of the CB surface—including directly on top of the incised signs—is an excellent indicator of the object's antiquity. Second, the dissolution processes that led to the formation of this patina also attest to the age of the object, in terms of the temporal context of its deposition. Since the terminus ante quem for which the process of dissolution of the CB serpentine began is at least 10³ years (Konrad et al. Reference Konrad-Schmolke, Halama, Wirth, Thomen, Klitscher, Morales, Schreiber and Wilke2018), we can confidently conclude that the object is pre-Hispanic in origin. Finally, dissolution that would result in the specific chemical characteristics evident in the CB can only occur in specific edaphological environments—conditions which align precisely with the humid, slightly acidic, saline soils common in southeast Veracruz. The most parsimonious explanation for these data is therefore that the original depositional context of the object was indeed the context in which it was reported to have been found (Rodríguez Martínez and Ortiz Ceballos Reference Rodríguez Martínez and Ceballos1999, Reference Rodríguez Martínez and Ceballos2007; Rodríguez Martínez et al. Reference Rodríguez Martínez, Ceballos, Coe, Diehl, Houston, Taube and Calderón2006). Taken as a whole, the data derived from pXRF analysis of the CB strongly support the authenticity of the object.

Comparative Analysis

The comparative pieces reported here were selected from the collections of the Universidad Veracruzana's Museo de Antropología de Xalapa (MAX, https://www.uv.mx/max), which houses one of the largest collections of Olmec art in the world. Although, as is the case with many Olmec objects, not all of the archaeologically known reference specimens come from controlled excavations with radiocarbon dating, INAH and international specialists have previously verified the authenticity of all of the reference specimens employed here as part of the incorporation of these objects into INAH's Registro Público Nacional de Monumentos y Zonas Arqueológicos e Históricos. We have focused on those objects that do have secure provenience and were recovered from systematic excavation or have reliable dates, such as La Mojarra Stela 1 and the jadeite object, greenstone celts, and figurines from Arroyo Pesquero, Veracruz (Wendt et al. Reference Wendt, Bernard and Delsescaux2014; Winfield Capitaine Reference Winfield Capitaine1988). The archaeological contexts and cultural affiliations of the comparative reference sample are therefore secure. The CB samples were evaluated against micrographs of the surface structure of modifications on over 70 Olmec stone objects in the MAX (and other) collections that were previously analyzed with the methodology employed here (Bernard and Melgar Tísoc Reference Bernard and Melgar2016, Reference Bernard and Melgar2018; Bernard et al. Reference Bernard, Melgar, Manrique and Ruvalcaba2018; Solís Ciriaco et al. Reference Solís Ciriaco, Melgar Tísoc and Lowe2016).

Samples were also compared against experimentally produced reference specimens created at INAH MTM's Experimental Archaeology and Lapidary Workshop. Since 2005, the workshop has employed experimental techniques to characterize the traces left by distinct manufacturing techniques used to produce ancient Mesoamerican lapidary objects (Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc and Solís Ciriaco2005, Reference Melgar Tísoc and Solís Ciriaco2009, Reference Melgar Tísoc, Solís Ciriaco, Crook, Edwards and Hughes2015, Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018). Since artifacts are fabricated and used in accordance with culturally specific criteria and schemes, the manufacturing process(es) used to create them leave characteristic traits (Andrefsky Reference Andrefsky2006; Ascher Reference Ascher1961; Braun et al. Reference Braun, Pobiner and Thompson2008; Eren et al. Reference Eren, Lycett, Patten, Buchanan, Pargeter and O'Brien2016; Laughlin y Kelly Reference Laughlin and Kelly2010; Lerner Reference Lerner, Chrisomalis and Costopoulos2013; Marsh and Ferguson Reference Marsh, Ferguson and Ferguson2010; McPherron et al. Reference McPherron, Braun, Dogandžića, Archer, Desta and Lin2014; Nami Reference Nami and Nami2010; Putt Reference Putt2015). The workshop seeks to replicate distinct types of modifications evident on archaeological objects, such as cuts, reductions, incisions, perforations, fretwork, and finishes (Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017:120, Figure 1; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc and Solís Ciriaco2009:120, Figure 2, Reference Melgar Tísoc, Solís Ciriaco, Crook, Edwards and Hughes2015:122, Figure 4, Reference Melgar Tísoc, Solís Ciriaco, Álvarez Icaza and Gonzalbo2017:268, Figure 18.1, Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018:646, Figure 19.22; Melgar Tísoc et al. Reference Melgar Tísoc, Solís Ciriaco and Ruvalcaba2012:107, Figure 7; Monterrosa Desruelles and Melgar Tísoc Reference Monterrosa Desruelles, Melgar Tísoc, Arroyo, Méndez and Ajú2017:915, Figure 6). It does so by using tools and materials available to pre-Hispanic groups, as identified in historical sources or in the archaeological record (Charlton Reference Charlton1993; Durán Reference Durán1967; Feinman and Nicholas Reference Feinman and Nicholas1995; Mirambell Reference Mirambell1968; Moholy-Nagy Reference Moholy-Nagy1997; Sahagún Reference Sahagún1956). To date, the workshop's reference collection encompasses 520 objects, produced with a variety of pre-Colombian lithic techniques, as well as modern tools, on various media.

In traceological analyses, features noted on reference specimens experimentally elaborated may be used to determine the techniques employed in the manufacture of archaeological materials. This is possible since the elaboration and use of lapidary objects produced under similar conditions and with the same techniques will leave characteristic patterns and differentiable features that can be compared against archaeological objects. Following interpretive criteria developed for the study of shell artifacts (Velázquez Castro Reference Velázquez Castro2007) and adjusted to lapidary objects, the workshop has identified the tools, materials, and processes most commonly employed in the manufacture of Mesoamerican lapidary objects (Table 3). Further, the workshop has identified several particular regional and temporal styles that characterize the lapidary production technologies of various Mesoamerican cultural groups, including Aztec (Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc and Solís Ciriaco2009, Reference Melgar Tísoc, Solís Ciriaco, Crook, Edwards and Hughes2015, Reference Melgar Tísoc, Solís Ciriaco, Álvarez Icaza and Gonzalbo2017; Solís Ciriaco and Melgar Tísoc Reference Solís Ciriaco, Melgar Tísoc, Alonso, Canales and Baena2017), Mixtec (Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco, Álvarez Icaza and Gonzalbo2017), Zapotec (Melgar Tísoc et al. Reference Melgar Tísoc, Solís Ciriaco, Licón, Tísoc, Solís Ciriaco and Licón2010), Teotihuacano (Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018; Melgar Tísoc et al. Reference Melgar Tísoc, Solís Ciriaco and Monterrosa Desruelles2018), Maya (Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017; Monterrosa Desruelles and Melgar Tísoc Reference Monterrosa Desruelles, Melgar Tísoc, Arroyo, Méndez and Ajú2017; Solís et al. Reference Solís Ciriaco, Melgar Tísoc and Lowe2016), and Olmec (Bernard and Melgar Tísoc Reference Bernard and Melgar2016, Reference Bernard and Melgar2018; Bernard et al. Reference Bernard, Melgar, Manrique and Ruvalcaba2018; Melgar Tísoc et al. Reference Melgar Tísoc, Solís Ciriaco and Monterrosa Desruelles2018; Monterrosa Desruelles and Melgar Tísoc Reference Monterrosa Desruelles, Melgar Tísoc, Arroyo, Méndez and Ajú2017; Solís Ciriaco et al. Reference Solís Ciriaco, Melgar Tísoc and Lowe2016), among others. These characterizations assist in the determination of cultural affiliations and temporal contexts for unprovenienced materials, since discrete cultures employed distinct lapidary toolkits at different points in time, which leave particular manufacturing traces on the objects.

Table 3.

Types of lithic modification and the tools and materials employed to create them.

For the purposes of this study, experimental reductions and incisions on Tehuitzingo serpentine—the same used for the pXRF analyses described above—were made with numerous abrasives and sharp-edged lithic tools, including flint flakes and obsidian blades, as well as chert, sandstone, limestone, andesite, and quartz. Sharp-edged tools were employed in this case since instruments with retouched edges leave thicker and coarser traces, which differ from the fine, superficial features evident on the CB. Polymer replica molds were created of these incisions and abrasions, following the methodology outlined above, then subjected to SEM analysis under the same parameters, and finally compared to micrographs of the CB samples. Micrographs of experimental pieces and CB samples were also compared against those of reference specimens from other lapidary traditions on multiple media (see, e.g., Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017:122–123, Figures 5–10; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco, Álvarez Icaza and Gonzalbo2017:274–279, Figures 18.5–18.9; Melgar Tísoc et al. Reference Melgar Tísoc, Solís Ciriaco and Ruvalcaba2012:111, Figures 12–14), including serpentine, jadeite, quartz, and other greenstones commonly worked by Olmec groups (cf. Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018:649–653, Figures 19.25–19.30). Thus, a large, diverse reference sample was employed to serve as the baseline against which the manufacturing traces on the CB were compared.

The fine, irregular, and diffuse lines of between 0.6 and 1.3 μm in width on the CB's inscribed surface revealed via SEM analysis (Figures 16, 18a, and 18b) are similar to those experimentally produced by obsidian tools (Figure 18c; see also Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017:122, Figure 7; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco, Crook, Edwards and Hughes2015:124, Figure 6a, Reference Melgar Tísoc, Solís Ciriaco, Álvarez Icaza and Gonzalbo2017:279, Figure 18.6, Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018:653, Figure 19.26) and distinct from those left by other materials, such as flint (Figure 18d; see also Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018:650, Figure 19.26), chert (Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017:122, Figure 8; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco, Crook, Edwards and Hughes2015:124, Figure 6d), modern tools (Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc and Solís Ciriaco2009:Figures 11 and 12; Walsh Reference Walsh2008:Figures 6–8), and other materials (Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc and Solís Ciriaco2009:Figures 6–13; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco, Crook, Edwards and Hughes2015:Figures 5–7). Comparing manufacturing traces on the CB incisions to those evident in archaeologically known incised materials from the Olmec nuclear area of the Gulf Coast (Figure 19), the patterns coincide. Several incised objects of Formative-period Olmec origin in the MAX collections, for example, previously analyzed with the methodology employed here (e.g., Bernard and Melgar Tísoc Reference Bernard and Melgar2016, Reference Bernard and Melgar2018; Bernard et al. Reference Bernard, Melgar, Manrique and Ruvalcaba2018), present identical manufacturing traces, with fine, irregular, and diffuse lines of the same width as those observed in the CB incisions. These include Las Limas Monument 1, an incised serpentine object from Jesús Carranza, Veracruz (Figure 19a); a greenstone celt from Arroyo Pesquero, Veracruz (Figure 19b); a jadeite object from Arroyo Pesquero (Figures 19c and 19d; Wendt et al. Reference Wendt, Bernard and Delsescaux2014); a greenstone figurine also from Arroyo Pesquero (Figure 19e); and the incised text of La Mojarra Stela 1 (Figure 19f; Winfield Capitaine Reference Winfield Capitaine1988).

Figure 18.

Comparative micrographs of Cascajal Block (CB) incisions and experimental manufacturing traces. (a) CB Sample 1. (b) CB Sample 2. (c) Experimental obsidian-on-serpentine incision. (d) Experimental flint-on-serpentine incision.

Figure 19.

Comparative micrographs of manufacturing traces on Olmec materials of known contexts. (a) Incision on Las Limas Monument 1. (b) Incision on a greenstone celt from Arroyo Pesquero. (c and d) Incisions on a mottled brown and white jadeite object from Arroyo Pesquero. (e) Incision on a greenstone figurine from Arroyo Pesquero. (f) Incision from text on La Mojarra Stela 1.

In the case of the unincised surfaces, the diffuse 10 μm bands and fine 3.5-μm lines noted on the CB (Figures 17 and 20a) are identical to those produced by the experimental abrasion of serpentine with sandstone (Figure 20b; see also Monterrosa Desruelles and Melgar Tísoc Reference Monterrosa Desruelles, Melgar Tísoc, Arroyo, Méndez and Ajú2017:915, Figure 7d). Such traces have also been identified on several Olmec objects of secure Middle Formative-period contexts at sites such as Arroyo Pesquero, San Lorenzo, La Venta, and Loma del Zapote (Bernard and Melgar Tísoc Reference Bernard and Melgar2018), in objects from the MAX collections such as Las Limas Monument 1 (Figure 20c; Bernard et al. Reference Bernard, Melgar, Manrique and Ruvalcaba2018), and even in objects from further afield, such as the incised celt with Olmec iconography from Chiapa de Corzo, Chiapas (Figure 20d; Solís Ciriaco et al. Reference Solís Ciriaco, Melgar Tísoc and Lowe2016). These patterns likewise differ significantly from those left by other reduction techniques characterized in previous experimental and traceological work, such as abrasion with basalt (Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco, Álvarez Icaza and Gonzalbo2017:274, Figure 18.5, Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018:654, Figure 19.31; Melgar Tísoc et al. Reference Melgar Tísoc, Solís Ciriaco and Ruvalcaba2012:11, Figure 12b), andesite (Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017:122, Figure 6; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018:649, Figure 19.25; Monterrosa Desruelles and Melgar Tísoc Reference Monterrosa Desruelles, Melgar Tísoc, Arroyo, Méndez and Ajú2017:915, Figures 7b and 7c), or limestone (Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017:122, Figure 5; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018:652, Figure 19.28; Melgar Tísoc et al. Reference Melgar Tísoc, Solís Ciriaco and Ruvalcaba2012:111, Figure 14b).

Figure 20.

Comparative micrographs of reduction and abrasion on unincised areas of the Cascajal Block (CB), experimental manufacturing traces, and reduction traces on Olmec materials of known contexts. (a) CB Sample 11. (b) Experimental abrasion of sandstone on serpentine. (c) Las Limas Monument 1. (d) An incised greenstone celt with Olmec iconography from Chiapa de Corzo.

The manufacturing traces evident on the CB and Olmec materials of known provenience thus coincide, suggesting that the CB incisions were made with sharpened obsidian tools and that surface reduction was realized via abrasion with sandstone, both common instruments and techniques in the pre-Hispanic lapidary toolkit. Although some of these reference specimens are comprised of materials others than the serpentine that constitutes the CB (e.g., jadeite [Figure 18c and 18d] or greenstone [Figures 18b, 18e, and 19d]), the same manufacturing traces are evident on all experimental and control reference specimens. Previous studies (Bernard and Melgar Tísoc Reference Bernard and Melgar2016, Reference Bernard and Melgar2018; Bernard et al. Reference Bernard, Melgar, Manrique and Ruvalcaba2018; Melgar et al. Reference Melgar Tísoc, Solís Ciriaco and Monterrosa Desruelles2018; Monterrosa Desruelles and Melgar Tísoc Reference Monterrosa Desruelles, Melgar Tísoc, Arroyo, Méndez and Ajú2017; Solís Ciriaco et al. Reference Solís Ciriaco, Melgar Tísoc and Lowe2016) suggest that Olmec lapidary technology is characterized in part by obsidian incision and sandstone abrasion, which differs from techniques evidenced in lithic artifacts produced by other Mesoamerican cultural groups (Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017; Melgar Tísoc and Solís Ciriaco Reference Melgar Tísoc, Solís Ciriaco, Crook, Edwards and Hughes2015, Reference Melgar Tísoc, Solís Ciriaco, Álvarez Icaza and Gonzalbo2017, Reference Melgar Tísoc, Solís Ciriaco and Manzanilla2018; Melgar et al. Reference Melgar Tísoc, Solís Ciriaco, Licón, Tísoc, Solís Ciriaco and Licón2010, Reference Melgar Tísoc, Solís Ciriaco and Monterrosa Desruelles2018; Monterrosa Desruelles and Melgar Tísoc Reference Monterrosa Desruelles, Melgar Tísoc, Arroyo, Méndez and Ajú2017; Solís Ciriaco and Melgar Tísoc Reference Solís Ciriaco, Melgar Tísoc, Alonso, Canales and Baena2017). Finally, Monterrosa Desruelles and Melgar Tísoc (Reference Solís Ciriaco, Melgar Tísoc, Alonso, Canales and Baena2017; see also Melgar Tísoc Reference Melgar Tísoc, Alonso, Canales and Baena2017) argue that these patterns are diagnostic of a specific temporal context, in which manufacturing techniques were standardized sometime prior to the Middle-to-Late Formative-period transition (ca. 700–500 b.c.), after which greater variability is evident in Olmec lapidary industries. We thus conclude that, from a technological standpoint, the CB was fabricated using the same lapidary technologies characteristic of the Early and Middle Formative periods evident on other Olmec objects of known contexts or recognized authenticity. These results therefore support interpretations of the CB as a product of the Olmec culture and bolster claims for its dating, further arguing for its authenticity. Finally, this research adds additional data that advances scholarly understanding of the lapidary technologies employed during the Middle Formative period, particularly among Olmec cultural groups.