Study of Calcite Crystallite Size as a Marker of Age in Stucco from the Archeological Site “El Cerrito,” Querétaro

This study examines calcite crystallite size variation as a potential chronological marker in ancient stucco from the “El Cerrito” archeological site in Querétaro, México. The pyramid, built in three unclear phases, provided a stucco sample measuring 6.9 cm wide and 8.8 cm long, consisting of five slices, each 1.38 cm thick, to analyze carbonation kinetics, from the back stucco (A-5L) to the front stucco (A-1L) of the pyramid wall. Two additional samples were taken from test wall stuccos prepared three years earlier using traditional materials: hydrated lime, pozzolan, sand, cotton, and nopal mucilage, as well as a stucco from a modern construction tested for 1, 2, and 18 months. X-ray diffraction (Rietveld refinement), infrared and Raman spectroscopy, and scanning electron microscopy were used to characterize the structural, chemical, and morphological features. Crystallite size ranged from 171 to 2568 nm, with the inner layer (A-5L) showing the highest values, reflecting distinct carbonation histories, humidity, and stucco porosity. For short periods of 1 to 12 months, the crystallite size remained nanometric between 44 and 68 nm. Raman and IR data confirmed carbonation gradients due to moisture transport, and X-ray diffraction (XRD) detected dominant calcite and kaolinite, with residual Ca(OH)2 in older samples.