Ornamental beads in a hunter-gatherers context from the Córdoba Province: a mineralogical and microstructural analysis of a “Borus” shell

Abstract

In this article, we analyze the mineralogical composition and microstructure of the “Borus” gastropod (Megalobulimus lorentzianus), which is local to the Córdoba Province. The gastropod was compared against a typical ornamental bead from a hunter-gatherers archaeological site located in the northwest region of the same province, with the aim of producing new tools to identify the raw materials used in bead manufacture. An X-ray diffraction analysis of a modern “Borus” shell specimen indicated that from a mineralogical standpoint it was composed entirely of aragonite, a calcium carbonate polymorph (CaCO3) that crystallizes in the orthorhombic system. In addition, an analysis of its microstructure using laser electron confocal microscope identified a prismatic microstructure. These same analyses, undertaken on a bead from the archaeological site of Alero Deodoro Roca (Ongamira valley, Córdoba Province) revealed the same mineralogical composition and prismatic arrangement, leading to interpret the bead as having a taxonomic affiliation to “Borus” shell. With the addition of new materials, in the future this type of analysis will provide insights regarding specialization in the elaboration of beads and exchange networks in the central region of Argentina.