The effects of surface weathering on the geochemical analysis of archaeological lithic samples using non‐destructive polarized energy dispersive XRF

Abstract

The purpose of this paper is to show the effects of lithic artifact surface weathering on whole rock non-destructive polarized energy dispersive X-ray fluorescence (P-ED-XRF) major and trace element determinations. Chemical results for a weathered and subsequently mechanically ground subset of New Hampshire Ossipee archaeological flakes, cataloged as hornfels, show that both groups of elements are variably affected by weathering. A graphic approach is developed and proposed to highlight the role and importance of immobile elements. A case is made and an analytical method is proposed for the routine use of P-ED-XRF spectrometers to determine the chemical makeup of lithic artifacts and therefore provide a data set compatible with existing geochemical databases and literature. The use of specific variation diagrams is adopted to portray the weathering trend. Internationally approved geochemical rock type diagrams are used to correct the rock type previously assigned to Ossipee artifacts and in turn narrow down potential quarry sources.

Assessing XRF for the geochemical characterization of radiolarian chert artifacts from northeastern North America

“…The method used in this study was developed at the Laboratoire de Caractérisation des Matériaux Archéologiques, Université de Montréal laboratory and is fully described in Gauthier and Burke (2011).…”

“…The same chemical element can play different roles in a mineral lattice; it can act as a network former in one type of mineral and fill the interstices in another type thus affecting its mobility. Gauthier and Burke (2011) have clearly shown that the effects of weathering on the non-destructive ED-XRF geochemical analysis of a weathered subset of New Hampshire Ossipee archaeological andesite flakes are considerable. The quartz dominant mineralogy of chert is expected to be more resistant to weathering than that of andesite, a ferromagnesian rich volcanic rock.…”

“…The analytical applications, used in this study, to determine major and trace element chert concentrations were optimized by using calibration curves comprising 20 international geological certified reference materials (CRM: USGS, GSJ, IGGE, CCRMP, NIST) and long counting times (see Gauthier and Burke, 2011).…”

“…This technique has already impacted the elaboration of well defined and internationally accepted chemical classification diagrams for volcanic rocks (Le Maître, 2002;Pearce, 1996;Middlemost, 1994;Le Bas et al, 1986. It also has been utilized by archaeologists in Canada and the USA to analyze jasper (Hatch, 1993;King et al, 1997;Stevenson et al, 1990Stevenson et al, , 1992, andesite (Gauthier and Burke, 2011), basalt Mills et al, 2008), felsite (Hermes and Ritchie, 1997), and obsidian (Hughes, 1983(Hughes, , 1988James et al, 1996;Shackley, 1988Shackley, , 1995Northwest Research Obsidian Studies Laboratory Reports, 1992e2011) artifacts. For a recent and more complete overview of X-ray fluorescence analysis in archaeology including a short history of XRF in archaeology, and the basic physics, mechanics and instrumental technology see Shackley (2011).…”

“…This study will show that a classic geology type geochemical XRF technique, using a modified non-destructive method (Gauthier and Burke, 2011), is well suited, firstly for the determination of the major and trace element composition of chert, and secondly for chert fingerprinting when the more robust and representative chemical elements are used for subsequent geochemical and statistical data treatments. Geological and artifact chert samples from outcrops, quarries, workshops and archaeological sites found in the lower St. Lawrence and Gaspé Peninsula (see Fig.…”