Description: New Zealand
Northern boundary: –34.1194851
Southern boundary: –48.9015311
Eastern boundary: 179.5011487
Western boundary: 165.1523805
Collections include artefacts that may date from the initial settlement by the ancestors of Māori around AD 1280 through the period of regular contact with Europeans after AD 1850.
Each artefact was assessed mid-z elements (Nb, Rb, Y, Zr, Sr) and other elements (Fe, Mg) using a pXRF and then matched to a geochemically distinct natural source of obsidian. Geographically ambiguous source assignments, such as assignment to a general volcanic zone, were not included. We note that out of the 15 known geochemically distinct natural sources of New Zealand obsidian , only 13 have been identified in archaeological collections.
The two university laboratories that produced this data each specified procedures in a series of publications. The specific lab protocols and machines used evolved over this period and so readers are directed to original studies for a fuller description. Examples of methods for Bruker pXRF, a type used in both laboratories, is summarised below.
University of Auckland
XRF analysis was carried out in the Roger Green Archaeological Laboratories, School of Social Sciences, University of Auckland, using either a Innov-X Alpha (see methods described in ) or a Bruker Tracer III SD portable X-ray Fluorescence (pXRF) analyser (see methods described in ).
The Bruker Tracer III SD instrument employs an X-ray tube with an Rh target and a 10mm2 silicon drift detector (SDD), with a typical resolution of 145eV at 100,000cps. The X-ray tube was operated with a setting of 40 keV at 10.7µA, through a window composed of 12mil Al and 1mil Ti filters (Bruker’s Yellow filter). Samples were analysed in an air path for 60 seconds. Each specimen was analysed twice on a different portion of its surface area to check for consistency and the values were averaged. A total of 12 elements were quantified (K, Ca, Ti, Mn, Fe, Zn, Th, Rb, Sr, Y, Zr, Nb). Concentrations were calculated as parts-per-million (ppm) using Bruker’s S1CalProcess (ver. 2.2.33) software. A set of 24 reference specimens are used for this calibration, including 18 international standards (AGV-2a, ANU-2000, GA, GSP-2, JA-1, JA-2, JA-3, JF-2, JG-1a, JG-2, JG-3, JR-1, JR-2, JR-3, NIM-S, NIM-G, NIST-278, QLO-1b) and six New Zealand obsidian specimens from the Anthropology Laboratory reference collection that were analysed using Wavelength Dispersive X-ray Fluorescence (AU-17.59, AU-29.16, AU-32.1, AU-7.21, AU-9.3, AU-9.5). Reference standard NIST-278 is routinely analysed to check for consistency.
University of Otago
XRF analysis was carried out at in the archaeology laboratories of the University of Otago using a BrukerAXS™ pXRF. All samples were shot using optimal settings for ‘mid-z’ trace elements (Rb, Sr, Y, Zr, and Nb), specifically 40kv and 8 or 25 microamps at a 300 second live time and with a filter (12milAl + 1milTi + 6milCu, or what the manufacture refers to as the ‘green’ filter). To examine lighter elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K), a second protocol was used that engaged the Bruker pXRF’s vacuum, with the beam set to 15kv and 45 microamps, but with no filter. For both settings, laboratory specific quantification protocols were created and applied. Linear regressions were based on nine pelletized international standards each shot three times for each of the two setting. Green filter linear regressions were improved by applying Speakman’s OB40 calibration to raw counts before the lab specific linear regression. A pelletized USGS basalt standard (BHVO-2) was run alongside samples as a quality check of precision and accuracy, with an additional second standard (SRM-278) run on the vacuum setting to check the pXRF performance over a range of values (ppm).
See original studies for details on collections and sampling strategies.
The two university laboratories produced quality control data based on international geological standards. The specific quality evaluations vary from study to study and so readers are directed to original studies for a fuller description. Examples of quality check results for Bruker pXRF, a type used in both laboratories, is summarised below:
University of Auckland: Comparison of calibrated results to accepted values for reference Standard NIST-278. All values are in parts-per-million (ppm). 
|pXRF Mean (n = 10)||34898||7221||1507||399||15113||53||13||131||65||40||288||17|
University of Otago: Comparison of calibrated results to accepted values for several reference samples. All values are in parts-per-million (ppm). Overall, values come close to published values and results for each setting produce comparable results. The exception is Th, which for this standard is near the limit of detection (LOD).
|Otago n = 43 (8 microamps)||1270||68332||116||2.2||10||378||24||159||16|
|Otago n = 7 (25 microamps)||1280||77388||101||0.6||12||371||25||164||17|
|Otago Lab, N = 3 (25 microamps)||419||13570||49||11.7||131||73||39||284||18|
As a check on accuracy on obsidians, an Otago lab standard Mayor Island Obsidian (AL380) is shown below as compared with published results from University of Auckland:
|Mayor Island Obsidian||Mn||Fe||Zn||Th||Rb||Sr||Y||Zr||Nb|
|Sheppard et al. (2011), pXRF||871||36942||194.2||n.r.||146.5||LOD||n.r.||1146.9||n.r.|
|AL380 Otago, XRF (25 microamps, solid)||718||30578||164||19.9||149||LOD||119||1184||101|
(3) Dataset description
Sourced Obsidian Artefacts, New Zealand, 2011–18. There are two files in the Digital Archaeological Record, (1) Master_list_NZ_obsidians _2011_2018.csv and (2) Supporting_Data_NZ_obsidians_2011_2018.zip. The master list gives source assignments by site. The supporting data lists any ppm and/or lithic technology information available and includes 28 files.
Most are secondary data; previously unpublished primary data referenced as “this study.”
Format names and versions
The data was created between 01/01/2011 and 09/18/2018.
Mark D. McCoy, Southern Methodist University
Ladefoged, Thegn N., University of Auckland
Geochemical Sourcing of New Zealand Obsidians by Portable X-Ray Fluorescence from 2011 to 2018. Mark McCoy. 2018 (tDAR id: 446766); DOI: http://doi.org/10.6067/XCV8C250CS.
Geochemical Sourcing of New Zealand Obsidians by Portable X-Ray Fluorescence from 2011 to 2018 (ppm/tech). Mark McCoy. 2018 (tDAR id: 446767); DOI: http://doi.org/10.6067/XCV87947N7.
The dataset is available on the Digital Archaeological Record (tDAR) repository.
(4) Reuse potential
Obsidian sourcing studies have become more commonplace since the widespread adoption of pXRF in archaeology. This dataset is the first national scale summary of artefacts definitively matched to source. It has excellent potential for future study regarding Māori culture history, social network analyses, and methodological development in the application of pXRF.