T167 Geochemical Geoarchaeology: Artifacts and Contexts

Tuesday, 20 October 2009
8:00 AM - 12:00 PM
E146

THE ELECTRON MICROPROBE AS A TOOL FOR THE RAPID AND MINIMALLY DESTRUCTIVE ANALYSIS OF VARISCITE ARTIFACTS

Paper number: T167-3
Program: Technical Sessions
Time: 8:30 AM – 8:45 AM

Authors

Abstract

Variscite (AlPO4·2H2O), also known as utahlite, lucinite, or amatrice, often has a color similar to turquoise and was commonly used for ornamentation by Fremont and later Indian peoples in the Great Basin. In fact, due to its similarity to turquoise, it may have often been confused with this mineral. Fe, Cr, and V are minor elements that act as chromophores.

We have characterized 4 potential variscite source localities in northern Utah: Fairfield and Amatrice Hill in Tooele County, and Lucin and Snowville in Box Elder County. Microprobe analysis reveals that Fe and Cr abundances are particularly good discriminators. A cross-plot of these elements separates the 4 sources with effectively no overlap, making it possible to clearly tie artifacts to source locations and ultimately infer trading patterns.

Minimal damage to small artifacts is accomplished by the use of 1” diameter plastic disc sample holders. Artifacts are placed into a hole drilled into the disc and then embedded in epoxy for later recovery by dissolution in methylene chloride. Hole diameters and artifact placements are chosen so that minimal grinding and polishing of the artifact is required.

20 nA and 20 μm beams were use to minimize readily apparent beam damage. Due to a lack of variscite microprobe standards, we calibrated Al & P on Lucin variscite, Si & Ca on wollastonite, Na on Jadeite, Cr on chromite, Fe on garnet, As on synthetic GaAs, and Co and V on metal alloys. This may produce systematic differences in “true” versus “apparent” abundances, but excellent reproducibility and source discrimination is achieved.