A CORRELATIVE MICROSCOPIC STUDY OF JASPER FROM SOUTHEASTERN PENNSYLVANIAN NATIVE AMERICAN JASPER QUARRIES: FINDING PERSISTENT CHARACTERISTICS OF STONE FOR TRACKING PREHISTORIC TRADE ROUTES

To understand how Native Americans moved across the landscape and reconstruct their trade routes, we need to understand the source of materials that they used. Native Americans in eastern Pennsylvania mined jasper from specific locations because the jasper at these sites was of high quality. The Cambrian Hardyston sandstone in Pennsylvania and New Jersey was locally brecciated and silicified near the basal nonconformity to form goethite-bearing brown jasper.

Because color and bulk chemical composition can vary within a single deposit, we analyzed microscopic characteristics of jasper from two quarries in the same geologic formation located 20km apart. Bulk-rock geochemical compositions of jasper are dependent on protolithic composition, geochemical nature of silicifying fluids, and subsequent degree of leaching by weathering solutions. We therefore analyzed thin sections and polished billets of jasper correlatively using a petrographic microscope and a scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) to document potentially robust microscopic features, including different types of intergrowths of goethite, quartz deformation lamellae, multiple stages of quartz veins, and the presence of minerals such as rutile, barite, apatite, and phlogopite.

The scanning electron microscope and optical microscope provide different but complimentary types of data. Although this is a preliminary study, several features observed in this study are robust enough to be seen in jasper artifacts and may ultimately permit the sourcing of artifacts to these quarries once the database of characteristics is more complete.