Esta es una síntesis de las principales características organizativas de la secuencia de explotación de la obsidiana verde del yacimiento de La Sierra de Las Navajas (Pachuca), de las culturas teotihuacana, tolteca y azteca. El uso de este vidrio volcánico se relaciona directamente con el desarrollo económico, militar, religioso y comercial de las organizaciones estatales del centro de Mesoamérica. En cada etapa cultural, identificamos los principales procesos de manufactura de instrumentos, armas y objetos religiosos en los talleres del yacimiento, así como la permanencia de los mineros, talladores y cargadores. El análisis diacrónico de la organización de la explotación y la distribución de la obsidiana verde con el desarrollo de la sociedad, nos permite detectar los cambios substanciales en la estrategía de obtención de esta importante materia prima.
The Cuicuilco pyramid was one of the first true urban centres in the Basin of Mexico. Its construction started a few centuries BC, during the Late Preclassic period. The pyramid is partially covered by a basaltic lava flow produced by the Xitle monogenetic volcano. New stratigraphic work around the pyramid and the volcano together with new radiocarbon dates indicate that the pyramid and nearby settlements were abandoned as a direct consequence of the volcanic activity of Xitle. The new dates, obtained from material which clearly is contemporaneous with the volcanic activity, suggest that the eruption took place around 1670 years BP, some 300 years later than previously thought.
The obsidian of Sierra de las Navajas is well known for its green color and gold hue. In order to relate these features with compositional and microtextural characteristics, we have carried out a microanalytical study by Wave Dispersion System associated to Electron Probe Micro-Analyzer, Scanning Electron Microscope observation, and X-rays micro-tomographic analyses of samples showing different colors (dark to light green, sometimes with bands of different color intensity) and hues (changing, uniform, no hue). In accordance with previous studies, the green color of the obsidian seems to be related to a high iron content, probably in its reduced state. However, no significant difference in composition occurs between dark and light green samples. The SEM observation and microtomographic study revealed the absence of microcrystals and the occurrence of vesicles of different size, shape, and orientation. Lighter green colors are shown by highly vesiculated surfaces, whereas non-vesiculated samples are darker. On the surfaces with a high concentration of coarse vesicles, a uniform golden hue is observed. Decreasing vesiculation gives a hue changing with the angle of incident light. However, when the vesicularity approaches zero, no hue is visible. The iso-orientation of vesicles along preferential directions and their distribution in bands determine the variation in color intensity and hue on differently oriented surfaces. Microvesiculation also influences other characteristics that were important features for the use of obsidian in the past, such as fracture, transparency, and roughness.
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