MINERALOGY AND PETROLOGY OF PALETTE STONES FROM ETOWAH MOUNDS, GEORGIA

Stone paletts are part of the artifact collection from the Etowah Mounds, near Cartersville in northwestern Georgia, and are known from other Mississippian chiefdom sites. Most palettes are round disks composed of greenish-gray rock, characterized as “greenstones” by archaeologists. Etowah palette stones from the Etowah Museum, the Smithsonian’s National Museum of the American Indian (NMAI) and the National Museum of Natural History were examined to determine the rock type used to make the palettes. Protocols for palette study restricted examination to nondestructive techniques (no cutting, breaking or grinding samples). Initial examination of the palettes revealed the palettes are composed of metamorphic rock with a strong foliation. The flat palettes are carved in the plane of this foliation. Relict bedding, defined by clastic grains of quartz and altered feldspar and darker, graphitic layers, is oriented at a high angle to the foliation in some palettes. One rectangular palette is composed of garnet muscovite feldspathic gneiss. Weathered pyrite is found in some of the graphitic layers and veins of barite cut the bedding and foliation in one sample. X-ray (XRF, XRD) examination of palette stones from the Etowah Museum collection were done on the whole disk using open-architecture instruments at the Metropolitan Museum. Results of the XRD studies generally confirm the mineralogy identified in hand samples and reveals the mineralogy of the aphanitic rocks. Quartz, albite, muscovite and chlorite are the major phases in the palettes; the gneiss is composed of orthoclase, albite, quartz and muscovite. Compositions of the palettes are elevated in Si, K and Rb relative to greenstones and are the same as Ocoee Group metasedimentary rocks that outcroup just east of Etowah. A more limited XRF analysis on a NMAI palette reveals an elevated Ba content, also consistent with a local Ocoee Group source. The gneiss palette contains a higher Si and K content than other palettes and is identical to composition to the Corbin Gneiss (a metagranite) that outcrops east of Etowah. The Etowah palettes are made of locally derived phyllite and metagranite and are not composed of greenstone.