heritage
Article
X-ray Fluorescence Spectroscopy of Picrolite Raw Material
on Cyprus
Theodora Moutsiou 1,2,3, * , Demetrios Ioannides 1 , Andreas Charalambous 1 , Sebastian Schöder 4 ,
Sam M. Webb 5 , Mathieu Thoury 6 , Vasiliki Kassianidou 1 , Zomenia Zomeni 7 and Christian Reepmeyer 1,2,3
1
2
3
4
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7
*
Citation: Moutsiou, T.; Ioannides, D.;
Charalambous, A.; Schöder, S.; Webb,
S.M.; Thoury, M.; Kassianidou, V.;
Zomeni, Z.; Reepmeyer, C. X-ray
Fluorescence Spectroscopy of
Picrolite Raw Material on Cyprus.
Heritage 2022, 5, 664–676. https://
doi.org/10.3390/heritage5020037
Academic Editors: Nikolaos Laskaris,
Georgios Mastrotheodoros, Maria
Kaparou and Artemios Oikonomou
Received: 27 February 2022
Accepted: 28 March 2022
Published: 29 March 2022
Archaeological Research Unit, University of Cyprus, P.O. Box 20537, Nicosia 1678, Cyprus;
ioannidis.dimtrios@ucy.ac.cy (D.I.); charalambous.c.andreas1@ucy.ac.cy (A.C.);
v.kassianidou@ucy.ac.cy (V.K.); christian.reepmeyer@jcu.edu.au (C.R.)
ARC Centre of Excellence for Australian Biodiversity and Heritage, College of Arts, Society and Education,
James Cook University, P.O. Box 6811, Cairns, QLD 4870, Australia
Department of Archaeology, Max Planck Institute for the Science of Human History, Kahlaische Strasse 10,
D-07745 Jena, Germany
PUMA Beamline, Synchrotron SOLEIL, Saint-Aubin BP48, F-91192 Gif-sur-Yvette, France;
sebastian.schoeder@synchrotron-soleil.fr
SLAC National Accelerator Laboratory, Stanford University, 2575 Sand Hill Rd., Mailstop 0069,
Menlo Park, CA 94025, USA; samwebb@slac.stanford.edu
IPANEMA, Synchrotron SOLEIL, Saint-Aubin BP48, F-91192 Gif-sur-Yvette, France;
mathieu.thoury@synchrotron-soleil.fr
Geological Survey Department, P.O. Box 24543, Lefkosia 1301, Cyprus; zzomeni@gsd.moa.gov.cy
Correspondence: tmouts01@ucy.ac.cy
Abstract: Picrolite artefacts comprise some of the most distinctive material remains in the prehistory
of the island of Cyprus, in the Eastern Mediterranean. Picrolite exploitation dates from at least
12,000 years ago for the manufacture of personal ornaments and items with a symbolic function.
It is commonly assumed that picrolite nodules were collected in secondary deposits on an ad
hoc basis. This narrative, however, ignores the fact that picrolite carriers can only be found in
very specific locations on the island, discrete from each other. Here we report initial outcomes of
the application of handheld portable X-ray fluorescence (HHpXRF) and synchrotron-based X-ray
fluorescence spectroscopy (SR-µXRF) to the analysis of picrolite raw materials performed at the newly
opened PUMA beamline of the SOLEIL Synchrotron Radiation Facility. Our work refines the basic
characteristics of the elemental constituents of the picrolite raw material and highlights key microstructural differences between two distinct source regions on the Troodos Massif in western Cyprus.
Picrolite source characterisation is expected to contribute significant new knowledge to the study of
rare raw material consumption, prehistoric social organisation, networking and possible long-distance
exchange of this idiosyncratic raw material within and beyond the island’s geographic boundaries.
Keywords: picrolite; X-ray fluorescence; synchrotron microspectroscopy; sourcing; Cyprus
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1. Introduction
Picrolite Use in Cypriot Prehistory
Anthropomorphic figurines in the shape of cruciforms dating to the fourth millennium
BC are the hallmark of the use of picrolite in Cypriot prehistory [1–3]. Although these
striking artefacts mark the epitome of consumption of picrolite on the island, the use
of this raw material in the manufacture of objects, such as ornaments, can be dated to
the earliest human presence on Cyprus (Figure 1). Picrolite artefacts, albeit in small
quantities, have been documented from Akrotiri Aetokremnos [4] on the southern coast of
Cyprus from stratigraphic contexts dating to ca. 12 kyr (~11,000 cal BC). The assemblage
comprises six picrolite objects: one bead, three pendants and two small pebbles, probably
pendant preforms.
Heritage 2022, 5, 664–676. https://doi.org/10.3390/heritage5020037
https://www.mdpi.com/journal/heritage
Heritage 2022, 5
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Figure 1. Picrolite artefacts from the island of Cyprus (from Akrotiri Aetokremmos, Krittou Marottou
Ais Giorkis and Kholetria Ortos).
The use of picrolite (Figure 2) has been subsequently well attested in Aceramic Neolithic (8900–5300 cal BC) sites, where the raw material was used to carve a range of
forms and types of objects: beads, rings, dress-pins, small vessels or containers as well as
items whose function remains unknown, such as the “thimbles” from Kritou Marottou Ais
Giorkis [5]. Occasionally, picrolite reaches archaeological sites in unmodified form, indicating the working of raw materials in settlement sites. Such occurrences are documented
across the island, for example in Ayia Varvara Asprokremnos and Khirokitia Vouni. In the
Late Neolithic, picrolite use was less common and the forms carved were less elaborate [6].
Picrolite exploitation was abundant during the Chalcolithic, when the highly distinctive
cruciform figurines were made. It was during this time that new carving techniques and a
substantial extension in morphology and stylistic repertoires occurred [6].
Figure 2. The map depicts the main picrolite carriers (including peridotite and serpentinite outcrops
with thin picrolite veins) on Cyprus. Blue dots indicate picrolite sample locations, while red dots show
Epipalaeolithic and Aceramic Neolithic archaeological sites with picrolite artefacts (1 = Khirokitia
Vouni, 2 = Kritou Marottou Ais Giorkis, 3 = Ayios Tychonas Klimonas, 4 = Apostolos Andreas Kastros,
5 = Kholetria Ortos, 6 = Parekklisia Shillourokambos, 7 = Kissonerga Mylouthkia, 8 = Kalavasos Tenta,
9 = Akanthou Arkosyko, 10 = Ayia Varvara Asprokremmos, 11 = Akrotiri Aetokremmos).
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Despite its long history of use and the high value [7] picrolite has enjoyed throughout
Cypriot prehistory, major questions regarding its acquisition patterns, circulation ranges
and social consumption remain unanswered. The main reason for this research gap is
the lack of data and understanding of the raw material and its sources that would enable
artefact provenance in a precise, accurate and systematic way. To date, little attention
has been paid to determining the elemental composition of picrolite raw material and,
crucially, the geochemical signatures of the various picrolite outcrops that occur on the
island. Applying high-resolution geochemical analysis, we expect to be able to achieve
elemental discrimination between distinct geological sources/subsources of picrolite. In
doing so, we would be able to contribute significant new data in the study of Cypriot
prehistoric heritage and open up new enquiries regarding the role of the island in regional
interactions within the Eastern Mediterranean.
Although stone has rarely been the subject of synchrotron radiation (SR), significant
outcomes can be achieved by the application of SR on this material category as well [8–13].
For example, Bernardini et al. [14] used SR-FTIR spectroscopy to analyse a set of serpentinite
polished shaft-hole axes dating to the transition from the Neolithic to the Copper Age in the
Caput Adriae region (northeastern Italy, central and western Slovenia and northwestern
Croatia). They were able to determine raw material chemical composition and used this
information to locate the primary sources of the serpentinite raw materials. Considering the
success of third-generation SR-based methods in supporting provenance issues in the field
of cultural heritage, this study applied SR-µXRF on picrolite raw material samples aimed
at achieving source discrimination/provenance by refining the chemical composition of
picrolite and defining micro-structures that may not have been identified through the bulk
geochemistry analysis by HHpXRF. Even though advanced SR methods are not the first line
of analytical techniques to be used in archaeological sciences, it is expected that its outcomes
can be used to inform/guide benchtop or portable methods (such as HHpXRF) that do
not have the spatial or energy resolution of SR-based techniques. When combined, these
techniques can, subsequently, be used to rapidly distinguish a large corpus of archaeological
and cultural heritage materials.
2. Background
2.1. Picrolite Raw Material
Picrolite is a soft, green massive, banded or crudely fibrous metamorphic rock with a
hardness of 3.5, a waxy feel and a conchoidal to subconchoidal fracture (massive), whilst
crudely fibrous varieties splinter easily [15]. Picrolite is the product of hydrothermal
alternation of ultrabasic rocks, consisting of the serpentine minerals lizardite, chrysotile and
antigorite, or any combination of these (for a discussion on serpentine mineral classification
see [16,17]). The Cypriot variant contains predominantly lizardite and/or chrysotile with
little or no significant proportions of antigorite. While serpentine (Mg, Fe, Ni, Mn, Zn)2-3 (Si,
Al, Fe)2 O5 (OH)4 mineral deposits are well documented around the globe, picrolite itself is
much less frequently encountered in a geological setting, e.g., [18].
In Cyprus, primary sources (seams) of good quality picrolite occur in the Troodos
Mountain Range and specifically east of the Mount Olympus summit at an elevation of
about 1400 m. Here picrolite is found in veins within seprentinised harzburgite; based on
geological observations it appears that serpentisation took place in situ, possibly after its
emplacement with little post-alteration penetrative deformation. Joints and fractures were
filled by chrysotile and picrolite and remained intact [19] p. 132. Picrolite veins, varying
in thickness from a few millimetres to a few centimetres and ranging in colour from light
blue-green to dark olive-green (GY7/10 light greenish grey to G6/5 greenish grey of the
Munsell Color Chart), can extend for several meters on Troodos’ north and south slopes.
The two main rivers—namely the Kouris and Karkotis Rivers—that drain the Troodos
Massif erode picrolite material, depositing it in pebble form on the north and south sides
of Troodos all the way to the sea. Serpentinite outcrops are also noted in the Limassol
Forest area, Akamas Peninsula, Mavrokolymbos and Diarizos and in other small serpentine
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bodies within the Mamonia Complex (Figures 2 and 3). In these instances, the outcrops are
heavily deformed and sheared in such a way that no usable vein material was produced.
Although picrolite veins are present, these are rarely more than a few millimetres thick and,
thus, unlikely to have been used by prehistoric people.
Figure 3. Picrolite in primary exposures (veins) and in secondary deposition (river pebbles).
2.2. Previous Analytical Studies on Cypriot Picrolite
Costas Manglis in [20] p. 441 was the first geologist who identified picrolite in archaeological contexts. Nevertheless, Xenophontos was the first researcher to analytically
investigate Cypriot picrolite [15,19] and his work, conducted thirty years ago, remains
the definitive study on picrolite raw material. Xenophontos applied neutron activation
analysis (NAA) and X-ray diffraction analysis (XRD) to determine its basic mineralogical
and geochemical characteristics [19]. For that he used thin sections from partly worked and
unworked waterworn picrolite pebbles found at the Aceramic Neolithic site of Kholetria
Ortos [21] and geological samples from the two main picrolite carriers, Kouris and Karkotis
Rivers. He further subdivided the picrolite raw material into three different textural types
see [19] (pp. 128–129), although no clear distinctions were made between source localities.
The new knowledge resulting from Xenophontos’ work had a direct and long-lasting
impact on the archaeology of Cyprus. Prior to his work, Archaeological artefacts made
of green stones and recovered from multiple archaeological contexts across the island
were invariably identified as ‘steatite’ [15]. Xenophontos demonstrated the inadequacy
of such broad-stroke characterisations of raw materials based on purely visual features
and documented the inclusion of picrolite in the raw material repertoire exploited by
prehistoric populations on Cyprus. However, despite the important change in terminology
and raw material association, little effort has since been placed in understanding picrolite
exploitation in Cypriot prehistory. The consumption of picrolite is commonly interpreted
as an expedient phenomenon, whereby the raw material was collected in pebble form from
secondary deposits (riverbeds) rather than being quarried from in situ seams in upland
locations (e.g., [6] but see also [22]). Although this may on occasion be the case, for example
a cache of 25 picrolite pebbles is known from Khirokitia [pers. obs.], the assumption that
all archaeological material derives exclusively from the nearest secondary deposits needs
to be tested. This is particularly important considering that multiple picrolite carriers occur
in various distinct localities across the island. Delineating primary picrolite outcrops, their
geochemistry and potential division into distinct geochemical units is likely to elucidate
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distinct acquisition and circulation patterns with important implications for the social
organisation of prehistoric communities.
3. Materials and Methods
3.1. Picrolite Geological Samples
Picrolite geological samples and in situ locales were initially analysed to collect elemental information (Table 1). Two surveys were conducted targeting primary outcrops
exposed at locations north and south of the Troodos summit, followed by further analyses
of secondary deposits at multiple localities along the two main rivers carrying picrolite
(Figure 2). With regards to the northern carrier, access to the sea was not possible, as the
area is currently outside the effective control of the Republic of Cyprus. We did, however,
sample material from as close to the northern coast/river mouth as possible. Selected
samples include primary deposits on the Mount Olympus peak of the Troodos Mountain
Range, and secondary locales along the two main carriers of Troodos, namely Kouris (south)
and Karkotis (north) Rivers. Serpentinite deposits with occasional picrolite exposures were
noted elsewhere, for example in Limassol Forest, but no samples were collected from those
locales since picrolite veins when they occur are of a size too small/thin to have been used
in antiquity.
Table 1. Picrolite geological samples from primary and secondary deposits from Cyprus analysed
with HHpXRF and SR-µXRF at the PUMA beamline at SOLEIL. Samples with multiple interesting
features underwent multiple analyses to capture the variability (see samples with asterisks *).
Source
Sample
Area
Source
Sample
Area
north
north
north
north
north
north
north
north (secondary)
north (secondary)
north (secondary)
north (secondary)
north (secondary)
north (secondary)
north (secondary)
north
agn_120.1
agn_118.2
agn_118.4
agn_119.2
agn_119.4
agn_120.2
agn_120.4
bri1_100.1
bri1_100.2
bri1_100.3
bri2_101.1
bri2_102.2
evr_102.1
evr_102.2
kan_117.4
square
transect
square
square
transect
square
transect
square
transect
square
transect
square
square
transect
transect
south
south (secondary)
south (secondary)
south (secondary)
south (secondary)
south (secondary)
south (secondary)
south (secondary)
south (secondary)
south (secondary)
south (secondary)
south (secondary)
south
south
south
south (secondary)
south (secondary)
south (secondary)
south
south
south
dex_110.16
epi3_103.2
epi3_103.1
epi8_105.3
epi8_105.4 *
epi8_105.4
epi8_105.4
epi8_105.4
eri6_104.1
eri6_104.4
eri7_107.1 *
eri7_107.1
kra_114.12
kra_114.13
lei_111.14
par_106.4 *
par_106.4
par_106.4
pla1_115.10
pla2_116.4
pyl_112.8
transect
square
rectangular
square
overview
overview
transect
vertical lines
square
square
square
square2
transect
square
transect
square
square
square
transect
square
transect
3.2. Sample Preparation
The samples were initially cleaned from surface contamination and sectioned to create
flat surfaces for HHpXRF analysis in the lab. Analyses were conducted on clean, fresh sectioned surfaces. For SR analysis, petrographic thin sections of picrolite geological samples
were prepared. The samples were mounted on quartz glass slides to minimise contamination. Evaluating the preliminary results from our earlier HHpXRF work, the 30 most
promising samples were selected for additional synchrotron analysis. For comparative
purposes, 15 samples from each region, i.e., north versus south, accounting for different
localities across each of the picrolite zones/carriers, were chosen. Figure 2 portrays known
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picrolite deposits in southwest Cyprus and locations of sample collection, highlighting
collection points in the context of this study.
3.3. Handheld Portable XRF (HHpXRF)
A handheld portable X-ray fluorescence (HHpXRF, Innov-X delta, now Olympus) spectrometer was used for the chemical analysis of multiple spots/areas at selected outcrops.
The specific instrument is equipped with a 4 W, 50 kV tantalum anode X-ray tube and a
high-performance silicon drift detector (SDD) with a resolution of 153–155 eV (Mo-Ka). An
Al filter (standard) with eight filter positions (automatic filtering) was used. The applied
analytical mode was Mining Plus. For this mode, beam 1 (40 kV) determines the heavier
elements Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Zr, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, W, Pt, Au,
Pb and Bi while beam 2 (10 kV) is used for the determination of Mg, Al, Si, P, S, Cl, K and
Ca (atomic numbers: minimum 12–maximum 83). Freshly cut sections were analysed three
to five times per sample. The time of analysis was 60 s. The beam size was 10 mm. In total
150 analyses were conducted on primary and secondary picrolite deposits. All data were
processed in MS Excel, which included calculating error ranges. The quantification is based
on a Fundamental Parameters algorithm designed by the manufacturer (Innov-X), with
results given as wt% and ppm in elemental form. Raw chemical analyses are provided in
Supplement Table S1.
3.4. Synchrotron Micro-XRF (SR-µXRF)
Preliminary assessment of the bulk chemistry obtained from the HHpXRF analyses
showed some overlap between sources, which limited the possibility to discriminate
unambiguously. Based on our analysis of a limited spectrum of trace elements (Mn, Cu, Co
and Sb), we assumed that this pattern of strong overlap was repeated in the general element
chemistry not accessible through conventional XRF. We chose at this stage an alternative
route to determine micro-structures in the sample material. To evaluate these preliminary
results and strengthen picrolite source discrimination, we opted for an additional set
of analyses of a much higher microscopic resolution/spatial sensitivity. Our particular
emphasis was on refining our preliminary bulk elemental analyses and investigating
potential micro-structures that may have remained un-identified via HHpXRF but are likely
to be key in achieving complete source discrimination.
The PUMA beamline at the SOLEIL synchrotron (Gif-sur-Yvette, France) is dedicated to the investigation of ancient materials and was developed in collaboration with
the IPANEMA platform (Institut Photonique d’Analyse Non-destructive Européen des
Matériaux Anciens) [13]. The PUMA (Photons Utilisés pour les Matériaux Anciens) beamline is a hard X-ray imaging beamline optimised for the scientific communities of the
heritage sciences that allows for 2D imaging capabilities with a microscopic spatial resolution, applying several analytical techniques including X-ray fluorescence spectroscopy
(XRF), on which this study is based. It generates photons using a 1.8 T wiggler insertion device with 8.98 keV critical energy. The beam is monochromatised with a Si(111)
double crystal monochromator. A KB-mirror optic focalises the X-rays into a spot size of
5 µm diameter.
The picrolite samples were analysed using µXRF spectroscopy. Spot selection was
based on distinct features noted on the samples after initial microscopy inspection at the
IPANEMA laboratory. The samples were mounted with an angle of 45◦ to the incident
beam, leading to an effective horizontal beam footprint of around 7 µm, and aligned with
the video-microscope of the beamline. A beam energy of 13 keV was used to allow for the
identification of the elements Ca, Ti, Cr, Fe, Co, Zn and As, at which the flux in the focal spot
was around 1E10 photons/s. X-ray fluorescence spectra were recorded with a silicon drift
detector (RaySpec Ltd., High Wycombe, UK) with a 100 mm2 active area (on a chip 80 mm2
collimated), a 450 µm-thick crystal and a 25 µm-thick Be window, installed at 90◦ from the
incident beam. A cylindrically shaped aluminium collimator with 8 mm internal diameter
and 10 mm length was used to reduce the spectral contribution of background scattering
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and unwanted signals from the sample environment. Detection limits of 0.1–100 ppm for
a 1 s measurement time and elements with an atomic number between 17 and 83 were
obtained for geological, biological and glass sample matrices [23].
XRF cartographies were performed on an area typically of 1 mm2 with 10 µm resolution
and an acquisition time of 1 s using the so-called flyscan routine, in which the sample is
moved continuously through the beam at a given speed and spectra are acquired over set
time intervals, and were corrected for their encoder motor positions before visualisation of
the data (see also [23]). The raw data are provided in Supplement Table S2.
3.5. Data Processing
The HHpXRF dataset was treated in a qualitative manner. In the cases where the
concentration of the elements was either absent or unsystematically represented to all
samples, the specific elements were excluded from the statistical treatment. Therefore, for
the statistical manipulation of the picrolite specimens the following elements were used:
Mg, Al, Si, Mn, Fe, Co, Cu and Sb. The extraction and inspection of SR-µXRF raw data was
conducted using the SMAK data processing software package developed by Dr Sam Webb
and available at SLAC [24]. For each elemental map, the number of counts for each element
under investigation was extracted and normalised to 100%.
Subsequently, the processed datasets of both HHpXRF and SR-µXRF were further
manipulated in Excel and statistically treated in MatLab. Principal components analysis
(PCA) was employed to visualise and explore the relationships between the elements of
north and south picrolite samples. The processed data were modified prior to running the
PCA in order to remove the dilution effect introduced by non-measured elements and give
approximately equal weight to all variables of interest. The standardisation followed here
follows the notation by Baxter and Freestone [25]:
(1)
yij ← xij − X j /S j
For the compositional matrix X made up of n cases and p variables, xij is the value for
the jth variable of the ith case, XJ is the mean value of the jth variable and Sj is the sample
standard deviation for the jth variable.
4. Results
4.1. HHpXRF Elemental Analysis
Multivariate statistical analysis of the dataset resulted in tentative source discrimination. Identification is based on the following major elements: Mg, Al, Si, Fe and, to a lesser
degree on the trace elements, Mn and Cu (Figure 4). Principal component analysis showed
that the first two eigenvectors explain 74% of the variance in the assemblage. There was a
strong positive correlation of northern outcrops with Mn, Fe, Cu, Si and Mg on the first
eigenvector and slightly negative correlations of Al on the first eigenvector. The second
eigenvector was positively correlated with Al, Mn, Fe and Cu, but was not unambiguously
able to separate the two source regions from each other. There were two clusters of samples
which were plotted in discrete regions, giving good discrimination; however, six samples
from the north (‘agn’ outcrops, and one ‘bri’ sample) and nine samples from the south (‘pla’
outcrops, two ‘epi’ samples, ‘dex’, ‘eri’ and ‘geo’) plotted close to each other, necessitating
further analyses to increase source discrimination.
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Figure 4. Principal component analysis (PCA) of picrolite elemental composition based on HHpXRF.
Red symbols correspond to samples from the north; blue symbols represent samples from the south.
4.2. SR-µXRF Elemental Analysis
μ analysis (PCA) was applied to the concentrations of the elements
Principal component
Ca, Ti, Cr, Fe, Co, Zn and As. These elements were selected to maintain a comparative
dataset with HHpXRF data (Supplement Table S1). The first two principal components
explain 76.6% of the total variance (Figure 5). Component 1 accounts for 52.2% of the
variance in the data and is characterised by high positive loadings of Ca, Ti, Cr, Zn and As.
Component 2, which accounts for 24.4% of the total variance, separates strongly on second
eigenvector where Fe is negative and Co positive. According to the multivariate analysis,
SR-µXRF increases the source discrimination based on the chemical composition of the two
major localities (i.e., north and
μ south), in that only five samples from the south (one sample
of each of the ‘pyl’, ‘par’ and ‘epi’, and ‘pla’ outcrops) overlap with samples from the north.
Samples collected from the northern slopes of the Troodos Massif are tightly clustered,
indicating a rather uniform elemental fingerprint. Conversely, picrolite specimens selected
from southern locales display significant chemical variability along the elements of PC1.
The sample collected from the southern locality Leivadi tou Pashia (lei 111.14) clusters far
from the rest of the assemblage along the PC2 axis. The sample is characterised by elevated
Fe and decreased Co content (GFe = 3.64, GCo = 4.31; GCrit = 2.76, a = 0.05) with respect to
the other southern picrolite specimens, indicating that it should be treated as an outlier.
The determination of sample lei 111.14 as an outlier has been established using Grubb’s
test for each element. The concentration of all elements within the assemblage follows an
approximately normal distribution.
Bivariate plots (Figure 6) of elemental ratios normalised to iron (Fe) display clustering
very similar to that of the samples in the PCA graph. The elements carrying the most
structure in the assemblage are Ca, Zn, As and to a lesser extent Ti, Cr and Co. The chemical
composition of the assemblage demonstrates that picrolite from the Karkotis River (north)
is richer in Co, while elevated values of Ca, Cr, Zn and As describe the picrolite found
following the course of Kouris River (south) (Table 2). Moreover, the analysis showed
that a small number of picrolite samples from the south overlap with the north group,
showing lower Ca, Zn, Cr and As values compared to the rest of the south group. The
samples of ‘epi’ which overlapped in the PCA show slightly higher Cr and As values.
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Higher Cr values are tentatively useful in separating ‘par’ samples from the northern
sources. Calcium appears to be higher in one of the ‘pla’ outcrops, which might lead to a
source discrimination. However, plotting the second set of ‘pla’ outcrops together with the
northern source samples and a discrimination was not possible.
Figure 5. Principal component analysis (PCA) of picrolite elemental composition based on SR-µXRF. μ
Red symbols correspond to samples from the north; blue symbols represent samples from the south.
Table 2. Average values of elemental ratios of picrolite normalised to iron (Fe). Note that all values
are multiplied by 1000.
North
South
Ca/Fe
Ti/Fe
Cr/Fe
Co/Fe
Zn/Fe
As/Fe
3.51
5.35
2.97
3.67
10.20
13.16
161.91
154.94
9.04
15.22
0.36
0.52
4.3. SR-µXRF Imaging
For additional analysis to identify possible pathways of source discrimination, SRµXRF was applied to confirm the existence of micro-structural differences amongst our
samples. As shown in Figure 7, a number of samples from the north group exhibited
clearly distinguishable circular features (inclusions) of about 100 µm diameter within
a largely homogenous matrix. These inclusions showed increased values of Fe, Co, Cr
and Ti and have been tentatively identified as chromium-magnetite phenocrysts. These
circular inclusions do not appear to be present in samples from the south group, which is
overall characterised by a more homogenous matrix. Interestingly, the occurrence of these
chromium-magnetite phenocrysts did not increase the overall Cr/Fe abundance of the bulk
chemistry; however, they were useful for discriminating between sources—for example,
the ‘agn’ and ‘bri’ outcrops that plotted together with the several southern samples in the
HHpXRF plot.
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Figure 6. Bivariate plots of elemental ratios of picrolite normalised to iron (Fe). The chemical
composition of the geological samples demonstrates that picrolite from the Karkotis River (north) is
richer in Co, while elevated values of Ca, Cr, Zn and As describe the picrolite found following the
course of Kouris River (south).
μ
μ
μ
Figure 7. SR-µXRF imagesμof picrolite samples (A) from the south (eri6-104.4, kra-113.14) featuring
lamellar structures; (B) from the north group (agn-102.2, agn-102.4) depicting clearly distinguishμ
able circular features (inclusions) of about 100 µm in diameter, tentatively identified as chromiummagnetite phenocrysts.
μ
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5. Discussion and Conclusions
The results obtained from the combined application of HHpXRF and SR-µXRF allowed
us to successfully refine the basic characteristics of the elemental constituents of the picrolite
raw material and capture key micro-structural differences between samples from two
distinct source regions on the Troodos Massif in western Cyprus. Portable XRF is now
an accepted method in archaeological research for the semi-quantitative and qualitative
determination of elemental composition predominantly as it allows geochemical analyses
to be non-destructive [26]. Non-destructive HHpXRF analysis showed the potential of
discriminating the two source areas; however, several samples showed strong overlap in
their respective geochemistry. The selected major elements Mg, Si, Mn and Fe and trace
element abundances of Cu were particularly useful in achieving source discrimination.
Unfortunately, two outcrops (‘agn’ and ‘bri’) were not unambiguously differentiated by
HHpXRF alone.
High-resolution SR-µXRF analysis and imaging was employed to enhance source
discrimination and applicability of non-destructive techniques. Multi-variate statistics of
SR-µXRF element abundances showed a tight cluster of northern sources with a clearer
separation of the two source regions using major elements of Ca, Fe and Ti with trace
elements of Cr, As, Co and Zn. However, again several samples showed overlap. Additional
high-resolution mapping of samples to identify possible micro-structures in the samples
was successful in identifying several round inclusions in the samples from outcrops ‘agn’
and ‘bri’. These inclusions were tentatively identified as chromium-magnetite phenocrysts
and occurred only in the northern outcrops. The round inclusion had a diameter of
approximately 100 µm diameter which is sufficiently large to be identified by analysis with
a microscope.
Well-designed archaeometric studies can provide useful information in the study of
ancient materials. The use of synchrotron radiation techniques to the study of archaeological
and cultural heritage objects has undergone a steep increase over the past ten years or so.
The methodology has been applied to a wide range of materials, including paintings, metals,
glass and organics, such as bone, teeth and wood. Stone has rarely been the focus of such
studies, particularly regarding the characterisation of raw materials for the manufacture of
stone tools and other lithic objects. The results obtained from the application of SR-µXRF
on picrolite samples add significant new data to the modest dataset of stone materials
analysed via synchrotron radiation techniques. Moreover, the application of a state-of-theart methodology with high spatial sensitivity (SR-µXRF) in combination with HHpXRF
confirm the effectiveness of the latter in characterising the overall chemical composition
of picrolite.
Distinguishing between different sources is crucial in filling significant research gaps in
the broader field of archaeology, including raw material selectivity, human mobility, social
communication and human–environment interactions. Within an Eastern Mediterranean
context, determining the geological sources of picrolite on Cyprus opens up new avenues to
address important questions on source utilisation in prehistoric Cyprus (e.g., [27]) and trace
patterns of exploitation diachronically. Moreover, having a detailed elemental signature of
the Cypriot picrolite sources opens up exciting new opportunities to investigate picrolite
exchange routes within and, crucially, beyond the island boundaries. Hundreds of artefacts
made of various ‘green stones’ are documented from the Levantine mainland (e.g., [28])
and remain, to date, unsourced. The possibility of at least some of these artefacts deriving
from either of the Cypriot picrolite sources is now a distinct research opportunity, with
exciting contributions to be made on key themes of global archaeological significance, such
as island colonisation and island–mainland interactions.
Supplementary Materials: The following supporting information can be downloaded at: https:
//www.mdpi.com/article/10.3390/heritage5020037/s1, Table S1: HHpXRF data; Table S2: SRµXRF data.
675
Heritage 2022, 5
Author Contributions: Conceptualization, T.M. and M.T.; methodology, T.M., M.T., A.C., D.I., S.S.,
S.M.W. and C.R.; software, D.I., S.S. and S.M.W.; formal analysis, T.M., A.C., D.I., C.R. and S.S.;
investigation, T.M., A.C., D.I., C.R., S.S. and Z.Z.; resources, M.T. and S.S.; writing—original draft
preparation, T.M., C.R. and S.S.; review and editing, T.M., A.C., D.I., C.R., S.S., V.K., Z.Z., S.M.W. and
M.T.; visualization, C.R., D.I. and T.M.; supervision, T.M., C.R., S.S. and S.M.W.; project administration,
T.M.; funding acquisition, T.M. and V.K. All authors have read and agreed to the published version of
the manuscript.
Funding: This work was funded by the Republic of Cyprus through the Research and Innovation Foundation (CULTURE/AWARD-YR/0418/0005) for the project Prehistoric Landscapes of
Cyprus (PLACe, 2019–2021). We also wish to acknowledge financial support from the Access to
Research Infrastructures activity in the H2020 Framework Programme of the EU (IPERION CH
H2020-INFRAIA-2014-2015: Grant agreement no. 654028) for the beam time. Professor Kassianidou
has also contributed funds from her research budget for this work.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available upon request from the
corresponding author. The data are not publicly available due to ongoing research.
Acknowledgments: We are grateful to the Geological Survey Department of the Republic of Cyprus
for permits and to SOLEIL and IPANEMA for providing access to their facilities and the synchrotron team.
Conflicts of Interest: The authors declare no conflict of interest.
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