PNNL

Abstract

Dark and clear silicate glasses formed during an iron age vitrification event ˜ 1500 years ago at the Broborg hillfort near Uppsala, Sweden have been analyzed using a scanning electron microscope equipped with a micro-X-ray fluorescence (?XRF) spectrometer. Correlated ?XRF and electron beam-induced energy dispersive spectrometry (EDS) X-ray maps were collected over an area covering tens of square millimeters at micrometer-scale resolution via stage-scanning at constant velocity. Overview images were used to select areas for EDS beam scan maps correlated with multispectral cathodoluminescence (CL) imaging and co-located quantitative EDS and ?XRF point analysis. Fe, Ca, Mg, Ti, P, Mn, Zr, Zn, and Y are enriched in the dark glass, while Si, Al, K, Na, Ba, Sr, Rb, and Ga are enriched in the clear glass. Unmelted material is comprised mostly of quartz (SiO2), minor Ca-rich feldspar (CaAl2Si2O8-NaAlSi3O8), along with trace apatite (Ca5(PO4)3[Cl,OH) and zircon (ZrSiO4). Multivariate statistical analysis was used to measure the area fractions of high variance components while lower variance components represented phase mixtures. Calculated melt viscosities for the glass compositions are consistent with field and laboratory observations. Coupled large area EDS and ?XRF imaging shows significant promise for informed selection of higher spatial resolution and higher sensitivity follow-up studies.