Mineralogical and mechanical characterization of a green stone pendant, from the archaeological site Nuevo Corinto, Costa Rica

Abstract

The green stones were objects of great importance within the pre-Columbian populations of the Costa Rican territory and were produced from year 500 BCE up to 900 CE. The green pendant studied belongs to the Terminal Period (700 to 900 CE) and was found in Nuevo Corinto archaeological site (L72-NC), located in “Línea Vieja” zone, in Central Caribbean of Costa Rica. The mineral composition of the pendant was determined by X-ray diffraction (XRD), which allowed to classify it as a “social jade” because its main mineral component is quartz. The state of conservation of the piece showed a lower mechanical stability determine by ultrasonic pulse measurements, and compared to samples of jadeite and quartz. This is possibly associated with postdepositional weathering processes of the site where the piece was located. At the same time, general morphological characteristics were observed through a combination of light microscopy and scanning electron microscopy (SEM), such as an irregular surface, where the orifices observed have a mayor presence of Fe and Al, while the smooth surfaces have a greater presence of Si, which is in agreement with the weathering processes observed. This study allowed a classification of the pendant, as well as to determine the state of conservation of the piece and the associated weathering processes.