PETROGRAPHIC CHARACTERISTICS OF ROCK SAMPLES FROM SELECTED ARCHAEOLOGICAL QUARRY SITES, CENTRAL NORTH CAROLINA PIEDMONT

This study involved the examination of hand specimens and petrographic thin sections of rock samples collected from known and suspected archeological quarry sites in the central Piedmont of North Carolina, mainly in the Carolina Slate belt. The objective was to characterize rock samples from each quarry and attempt to establish a basis for distinguishing quarries. If quarries can successfully be distinguished, then possible sources for prehistoric artifacts found elsewhere might be determined. In the first phase of the project, 53 samples were examined. 26 of these samples are from the Uwharrie Mountains region; many of these were collected and described previously by Daniel and Butler (1996). 30 additional specimens were collected from other quarry sites in the Carolina terrane in Chatham, Durham, Person, and Cumberland Counties. A companion project is examining chemical characteristics of the quarry sites.

Rocks include both metavolcanic and metasedimentary types. Compositionally, most metavolcanic rocks are dacitic, but they include flows, tuffs, breccias, and porphyries. Metasedimentary rocks are metamudstone and fine metasandstone.

Quarries may be grouped into one of several different petrographic categories, based on textures and minerals. Relict volcanic textures include porphyritic texture, flow-banding, amygdules, inferred glass shards, spherulites, and pyroclastic material, while relict sedimentary textures include laminations, ripples, and graded bedding. Metamorphic textures include phyllosilicate cleavage. Relict minerals are quartz, plagioclase, and possible K-feldspar phenocrysts; metamorphic minerals include chlorite, biotite, epidote, calcite, actinolite, titanite, pyrite, garnet, stilpnomelane, and piedmontite.

Daniel and Butler identified four quarry groups from the Uwharries, based primarily on phenocryst assemblage. This project corroborates and extends their results to six quarry groups, and demonstrates the potential usefulness of metamorphic mineralogy in sourcing lithic artifacts in the region.