Iron-Ore Mirror Exchange in Formative Mesoamerica

One of the most interesting discoveries made at la Venta, Tabasco, was a series of large, parabolically conclave mirrors made of three types of iron ore: magnetite, ilmenite, and hematite (Drucker, Heizer, and Squier 1959). Garniss Curtis (1959), who determined the gross petrological characteristics of the mirrors, placed their probable point of origin somewhere in the “metamorphic and granitic province” of the state of Oaxaca (Curtis 1959: Figure 80).

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In order to simply the referencing of spectra, the iron ores studied by Mössbauer analysis were divided into the following five general groups: I, samples composed mainly of magnetite; II, samples of relatively pure hematite; III, samples of ilmenite; IV, samples containing a mixture of magnetite and ilmenite, and V, samples composed of a mixture of magnetite and hematite.

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Group I-A is a quite pure magnetite which presents inclusion-free faces ideally suited for mirror making. It includes 10 Early Formative ore lumps or mirror fragments form San José Mogote, Oaxaca, and 1 Early Formative ore lump traded to San Pablo, Morelos. The spectrum matches ore from the twin sources of Loma de Cañada Totomosle-Lomade la Visnagra, near Santiago Tenago, 27 km north of San José mogote (Figure 10.13).

Group 1-B is a magnetite with slight ilmenite contamination, very compact and suitable for mirror making. Its spectrum mathche sthe source at Loma los Sabinos, near Simatlán, 33 km south of San José Mogote. The group includes five Early Formative lumps or mirror fragments from San José Mogote, one sample from Coyotepec in the Valley of Oaxaca, and one mirror traded to Etllatongo in the Valley of Nichixtlán, Oaxava (Figure 10.13).

Group I-C consists of a single large, concave, scalloped-edge magnetite mirror from Middle Formative La Venta, whose spectrum does not match any source we have collected.

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Group IV-A is a mixed magnetite-ilmenite of low quality form a source at Loma del Arroyo Terror near Arrazola, just off the western slope of Monte Albán in the Valley of Oaxaca, Mogote, but apparently not converted into mirrors; a single lump also occurred at Tierras largas, only 8km from the source.

Group IV-B is a mixed magnetite-ilmenite whose spectrum matches the source exposed on the surface and in arroyo profiles at Loma Salinas near San Lorenzo Cacaotepec, only 7 km southwest of San José Mogote, Oaxaca. The group includes a partly worked ore lump from Jan José Mogote and two small flat mirrors evidently traded to San Lorenzo, Veracruz, during the Nacaste phase (Figure 10.14)

The Early Formative: Magnetite Mirrors as an Item for Elite Exchange

By far the majority of Early Formative archaeological samples were either magnetites or mixed magnetite-ilmenites form sources in the Valley of Oaxaca. The bulk of the samples examined came from San José Mogote, the largest site in the Valley of Oaxaca during this period. A surface survey of the site revealed a striking, 1-ha concentration of iron ores—more than 500 pieces which had evidently been collected from various iron sources in the valley. Excavations within this area (Area A) exposed a series of four super-imposed household clusters (numbered C1 through C4) and associated midden deposits. Whole and broken magnetite mirrors, unfinished mirrors, and worked and unworked lumps of iron ore were found together in these household clusters. Comparative examination of the finished and unfinished mirrors reveals a similarity in size, shape, and grinding technique. The typical produces are thumbnail-size, flat-surface mirrors of various sides. Traces of multi-directional grinding are discernible on the unfinished and roughly finished sides of the mirrors. Closer examination of the mirror surfaces reveals some traces of ochre in surface irregularities, indicating that this substance may have been used to obtain the high polish of the finished products. It is not known for what the mirrors served, but evidence from figurines at Tlatilco and La Venta suggests they were worn on the chest, possibly by individuals of some special status. Some of the Oaxaca mirrors may have been worn as inlays in ornaments of pearl oyster shell, judging by some broken specimens found at Area A of San José Mogote (Figure 2.14h).