SOURCE DETERMINATION OF OBSIDIAN 
FROM THE WESTFIELD (R11/898) SITE 
USING GEOCHEMICAL ANALYSIS 
R. S. RUDDOCK 
GEOLOGY DEPARTMENT, UNIVERSITY OF AUCKLAND, AUCKLAND 
Abstract. Non-artefact obsidian from the Westfield (R11/898) site was sourced using X- 
ray fluorescence (XRF) chemical analysis on seven flakes of unknown origin and 
selected geological samples of known source, Both qualitative and quantitative methods 
of clustering the unknowns indicates that the obsidian from this site comes from as few 
as two sources. Mayor Island is the most likely source of the green obsidian, and it is 
likely that most of the grey unknowns came from a Great Barrier Island source. Within 
the constraints of possible error, the idea of only two sources fits accepted theories on the 
origin of this raw material for temporary sites on the Auckland isthmus. 
The results of the excavation of the Westfield (R11/898) site are outlined by 
Furey (1986). She concludes that this was a temporary camp within an area of 
gardening. An age range of 309 + 59 to 421 +59 years B.P. is indicated by radiocarbon 
dating. Cultural remains occur in three main stratigraphic layers, and two occupation 
periods are recognised. A range of artefacts were collected, including a total of 626 
obsidian pieces (forming some 52% of the lithic material, Furey 1986). This obsidian 
was Classified according to colour, as shown in her Table 1, with the note that “. . . the 
green flakes are probably from Mayor Island and the grey obsidian is likely to be from 
several sources,” (Furey 1986:18). This paper outlines an attempt to provide a more 
quantitative basis for the sourcing of this obsidian. 
Sample selection 
Two hundred and fifty two non-artefact pieces of obsidian from site R11/898 
held at the Auckland Museum were used in this study. These pieces were assigned to 
one of the three designated stratigraphic layers, with 85 pieces having no layer 
assigned to them. A preliminary sort was then carried out on the basis of the series of 
hand specimen parameters shown on the flowchart of Moore (n.d.). In practice the 
colour (especially transmitted) was the major determining factor in this sorting 
process, mainly due to the small size of the obsidian pieces. 
Two major considerations influenced the choice of samples to be analysed by the 
x-ray fluorescence (XRF) method: 
(1) sample size, ideally 10 grams of material is required, this was rarely achieved 
in the given sample set. 
Rec. Auckland Inst. Mus.25: 49-56 19 December 1988 
