A geoarchaeological methodology for sourcing chert artefacts in the Mediterranean region: A case study from Neolithic Skorba on Malta

This article introduces a robust scientific methodological approach that has been effective on accurately sourcing prehistoric chert artefacts. The research focuses on the lithic assemblage of Skorba, a late Neolithic site of Malta, and local chert rock sources. This assemblage is mainly consisting of chert tools and artefacts, but the origin of the raw materials remains inconclusive. Although chert outcrops are reported on Malta, they have yet to be investigated and their petrological characteristics are unknown. Moreover, it was always assumed that nonlocal chert material has been only imported from Sicily. This, however, remains at a theoretical level and elaborate provenance research is necessary to test it. This archaeological background serves an excellent opportunity to employ an interdisciplinary methodology and address uncertainties that conventional archaeological practices seem unable to provide clear answers. This methodology includes geological techniques that focus on petrological and geochemical characteristics of chert formations. The collected results provide the necessary scientific evidence to connect some artefacts with their actual sources and provided useful information about the possible origin of others. This paper further aims to demonstrate the great prospects of this suite of techniques and its suitability for similar provenance studies of chert material worldwide.


| Chert as raw material
Cherts are fine-grained, dense and very hard sedimentary rocks, which are composed predominantly of silicon dioxide (SiO 2 ) minerals (>90%). They break with a conchoidal fracture, often producing very sharp edges and variations in colour. Cherts are common but not abundant rocks in the geologic record, which range in age from the Precambrian to the Quaternary (Boggs, 2009;Tucker, 2001). The origin of SiO 2 is considered to be either entirely biogenic or a product of hydrothermal activity (Maliva, Knoll, & Simonson, 2005;Shen et al., 2018).
They are typically composed predominantly of Si, but can include other major elements such as Al, Fe, Mn, Ca and Ti (Luedtke, 1992).
In addition, cherts also contain minor amounts of trace (e.g., Sr and Th) and rare-earth elements (REEs). Mineralogically, they mainly consist of quartz, but other polymorphs of silica have been reported (e.g., Opal-A). Lastly, the chert outcrops are commonly found intercalating host formations such as limestone, and they appear in the bedded or nodular form.

| Chert versus flint debate
The literature on Maltese prehistory (Malone, Stoddart, Bonanno, & Trump, 2009;Vella, 2008a,b) has used a variety of terms-chert and flint-to describe relevant lithics recovered from the sites. Archaeologists typically call flint the very fine-grained, homogeneous, with shiny lustre siliceous materials and everything else chert. Geological research, however, has allocated specific petrological characteristics to each of these terms (Boggs, 2009;Tucker, 2001) and a proper geological investigation is necessary before choosing the appropriate one.
Chert is a general geological term used to define all concretions, nodules and tabular layers of amorphous siliceous precipitate dominantly composed of SiO 2 . In addition, it is not age-specific and can occur throughout the stratigraphic column. In contrast, flint is an informal geological term and its use must be restricted to a specific variety of amorphous SiO 2 originating within the northwest European Cretaceous chalk formation.
Although there have been important attempts to bridge the gap between disciplines (Brandl et al., 2018;Högberg & Olausson, 2007;Luedtke, 1992;Přichystal, 2013), these terms are still used outside their original context creating confusion. A petrologically focused paper is thus more appropriate to resolve the exact type of material found in Malta and Sicily. Until then, "Flint" (frequently misused in an archaeological context) is not an appropriate term for use in this study. This paper will use the term "chert" throughout, which with respect to geology, encompasses all the similar types of this rock formation.

| The prehistory of Malta
Archaeological research has found evidence of a highly advanced preurban community on the Maltese Islands (Malone et al., 2009;Vella, 2009). The earliest evidence for human occupation goes back to the early Neolithic period, which would now be placed at c. 5,800 to 5,500 BC, thanks to the dating program of the ERC-funded FRAGSUS (Fragility and sustainability in restricted island environments: adaptation, cultural change and collapse in prehistory) project. This date range is also considered as the onset of the Pre-Temple early Neolithic period of the Maltese Islands, which lasted until c. 4,100 B.C. The Pre-Temple period encapsulated sites of human occupation in open areas and caves. The stone temples were constructed and modified over a lengthy period from ∼3,800 to 2,300 BC (Malone et al., 2009).
In association with these late Neolithic sites, important chert assemblages have been discovered during a succession of excavations in the late 20th and early 21st centuries (e.g., Evans, 1971;Trump, 1966Trump, , 2015FRAGSUS). Some preliminary works (Malone et al., 2009;Vella 2008aVella ,b, 2009) on these finds suggest that most of these finds are derived from local chert material. In addition, they reported many artefacts, which are related to nonlocal chert rocks.
There is an existing theory suggesting a Sicilian origin, based on the proximity of Sicily with Malta and the known chert outcrops of this island (Vella, 2008a). However, there has not yet been a proper sourcing investigation and these findings are mainly based on macroscopic examination of these assemblages. The uncertainty of these statements increases with the fact that the local chert-rocks have never been investigated in geological and archaeological terms. This paper focuses on the chert assemblage recovered from the late Neolithic site of Skorba (Temple and settlement). It reports on provenance research that used a holistic geological methodology to test the current theory and presents the results on the origin of these chert finds.

| Skorba temples (stone temple and settlement site)
This archaeological site is found in an area called Li Skorba, near Mġarr village, which is located in the Northwest of Malta (Figure 1).
The existence of the site was first reported in 1937, while proper excavations were conducted between 1961 and 1963 (Trump, 2015).
They were conducted using modern methods of dating and analysis, which provided reliable and significant data. The Skorba temples are composed of two adjacent temples (West and East temples) of the well-known Maltese prehistoric type (Trump, 2015). The West CHATZIMPALOGLOU | 899 temple is the oldest, while the East presents a different structure ( Figure 2). The early temple consists of three apses opening from a court, while the latter one is composed of four apses in two opposed pairs connected with a corridor (Trump, 2015).
During the excavation of the temples (1961)(1962)(1963), a settlement was discovered, which was established well before the erection of the temples. It is considered one of the very few known Neolithic-Bronze Age site (Trump, 2015). This has provided a detailed and informative insight into the earliest periods of Malta's Neolithic culture, allowing this study to consider the entire span of the Maltese Neolithic period between 5,600 and 2,300 BC. The Skorba temples are one of the six megalithic temples in Malta listed as a UNESCO World Heritage Site.

| Field research
The investigation on the Maltese Islands (2016 and 2017) was separated into two parts: (a) indoor macroscopic examination of the assemblages and (b) fieldwork to investigate for chert outcrops and collect samples. The latter work included detailed mapping of the chert sources and macroscopic examination of the chert outcrops and assemblages. The outdoor investigation followed the baseline provided from the Geological Map of Malta (Pedley, 1993), and was aided by Pedley himself. Throughout the two field campaigns, 33 samples were collected for studying the mineralogy and geochemistry of the rocks.
The number of samples collected from each outcrop is always related to the extend of the exposure, the variability reported on the field of the investigated formation and the quality of the outcrop.
The examination of the Neolithic chert assemblage from Skorba was conducted in its storage locations in Malta and 150 representative samples were selected from further laboratory investigation.
The macroscopic examination followed the baseline of the work provided by Crandell (2006) and Luedtke (1992). Seven macroscopic characteristics were examined: colour, fabric, translucency, lustre, grain, pattern and cortex. The colour of the artefacts and raw materials was described with the help of the Munsell Rock Colour Book (Munsell, 2014).
This increased the accuracy of the colour description and minimised the subjectivity of the researcher. The other six features followed the terms and explanations provided in the work of Crandell (2006). The fabric could be homogeneous or heterogeneous, while the translucency was described as highly translucent, translucent, subtranslucent or opaque.
The lustre could be termed shiny, medium or dull and the size of the grains which was described as fine, medium or course. The pattern refers to the distribution (whether even or uneven) of colour, grain, lustre and translucency (Crandell, 2006), which is divided to spot and linear categories. The last category recorded (i.e., cortex) the existence of cortex residues on the samples, which indicated the host rock formation (e.g., limestone) of the original outcrops. This stage was followed by employing a suite of laboratory methods (presented below) on the collected samples (geological and archaeological) to draw conclusions about the chert formations of Malta and the chert assemblage from Skorba.

| Laboratory research
The laboratory work started with the preparation of 50 rock slices for macroscopic evaluation of the rock samples on a fresh surface and re-evaluation of the macroscopic characteristics of the archaeological samples. Re-evaluating the macroscopic characteristics helps to minimise the errors occurring within the intense period of fieldwork. The slices were prepared in the Charles McBurney Laboratory for Geoarchaeology, based in the Department of Archaeology at the University of Cambridge. This was followed by Fourier transform infrared-attenuated total reflectance (FTIR-ATR) analyses that were conducted in the same laboratory. The equipment of this method has basically two parts (heads): (a) FTIR and (b) ATR. The first requires powder samples to conduct an analysis and is considered more accurate, while the second can perform measurements on flat surfaces (if available) but is less accurate. Flat surfaces, however, is difficult to find on an artefact and the need of powder samples cannot be avoided. ATR though does not require the same amount of powder (minimal invasive) and the accuracy of the results are increased.
Representative FTIR spectra obtained from all rock samples (n = 33) by grinding a few tens of micrograms of the sample using an agate mortar and pestle (Parish, Swihart, & Li, 2013;Smith, 2011). About 0.1 mg or less of the sample was mixed with about 80 mg of KBr (IR-grade). A 7-mm pellet was then made using a hand press and the spectra were collected between 4,000 and 400 cm −1 at 4 cm −1 resolution, using a Thermo Nicolet 380 spectrometer. The rock samples were also examined with the ATR equipment to have a solid cross-reference database between the two techniques.
The analyses on these samples were performed on flat surface and on powder samples to test the limitations of the equipment.
This served as an internal standard of the technique for reducing errors, overcoming the possible lack of mineral reference and securing accurate interpretation of the ATR spectra. A similar (i.e., 0.1 mg) or less sample was used to collect ATR spectra, again F I G U R E 2 Simplified plan of the Skorba temples [Color figure can be viewed at wileyonlinelibrary.com] between 4,000 and 400 cm −1 at 4 cm −1 resolution. The artefact samples (n = 100) were only analysed with the ATR equipment to minimise the impact of this method. The ATR spectra were obtained under the same conditions as the rock samples and the measurements were performed on powder sample because flat surfaces were difficult to detect.
Elemental analyses were performed using the Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) technique to determine the composition of the major, trace and REEs (Neff, 2012;Speer, 2014). The equipment was based in the Department of Earth Sciences at the University of Cambridge. Through this method, 24 rock and 60 archaeological samples were examined. The samples were placed, with the flat surface on top, in a case below the laser beam. A 100-μm diameter laser beam, a laser repetition rate of 10 Hz and a laser power of 8 J/cm was used for the entire study.
In addition, approximately 1 μm of the top surface was removed using preablation to avoid any surface contamination. The ICP-MS data acquisition settings in the Syngistix version 1.1 software were 1 sweep per reading, 60 readings, 1 replicate and total data acquisition lasted 44 s in peak hopping mode. The data were acquired at a rate of one point for each element every 0.75 s. For all analyses, NIST614 was used for calibration of element sensitivity using the "Preferred Values" (Ref 1 published on the GEOREM database). Calibration accuracy was checked by analysing the NIST610, NIST614 and BCR-2G standards at the beginning, end and periodically within each laser session.
For data processing and calculation of concentrations, Glitter Software (GEMOC, Australia) was used to process the raw data files containing the signal intensity versus time data (the output from the Elan software). This allows precise selection of blanks, signals and rapid visualisation of the intensity data. A minimum of four measurements were taken per sample and the results of those that passed the error criteria (i.e., Error < 20%, RSD < 5% and 95% < REC < 105%) were averaged. The overall process of the results and the subsequent geochemical models were conducted with the use of the software GCDkit (ver. 3).

| RESULTS
This chapter presents the results from each technique of the proposed methodology. Tables 1-4 present the results of the main samples discussed in this paper, while the full volume of the results, data and interpretations can be found in the work of Chatzimpaloglou (2019).

| Maltese chert source
The existence of the chert outcrops has been long reported (Cooke, 1893), but little is known about their characteristics and the conditions under which they formed. Archaeological research suggests that these chert rocks were used by the prehistoric inhabitants (Malone et al., 2009;Vella, 2009) and a better understanding of these resources is necessary. The chert outcrops are found within the middle Globigerina Limestone formation (M. Pedley & Galea, 2002), which has extensive exposures in the islands of Malta and Gozo. The fieldwork (Chatzimpaloglou, 2019) revealed that chert outcrops are present only on the western parts of these islands (Figure 1b (Table 1). Continuing downhill, the silicate deposits increase in size and frequency, forming beds ( Figure 3c). They extend over a distance greater than 10 m and four samples have been collected (G2S3, G2S4, G2S5 and F1S4). They are mainly heterogeneous, opaque and coarse-grained, with a significant presence of calcium carbonate (CaCO3). They are olive-grey (5Y 3/2) or dusky-yellow (5Y 6/4) in colour, dull and occasionally laminated and/or splotched (Table 1). At the lowest points of the stratigraphy, the chert outcrops reshape into nodular forms. They are homogenous and fine-grained but differ from the previous cherts Irregular shape spot pattern that covers less than 30% of the sample's surface (Crandell, 2006).

| 901
The investigation has found mainly nodular chert (samples M2S2 and M2S3) but also some bedded cherts (sample M2S4). They present similarities in fabric and translucency but differ in the other macroscopic characteristics (Table 1).

| Skorba chert assemblages (SKB16)
The Skorba assemblage (SKB) was collected during the small trench excavation of the prehistoric settlement (2016), which is located on the west side of the Skorba Temple. This study has revealed a sig- Focusing on the chert members of the assemblage in terms of sources ( Figure 5), they are mainly divided into two groups. The first group of artefacts is characterised by fine-grain size, spot patterns and the absence of translucency (i.e., opaque) and shine (i.e., dull). The main recorded pattern is described as spotted (Crandell, 2006) because they exhibit irregular shapes of white spots on their surfaces.

| Mineralogical examination
The mineralogical content of the rock sources and artefacts was investigated with the FTIR-ATR equipment (Tables 1 and 2). There is already important research (Chukanov, 2014;Hawkins, Tourigny, Long, Julig, & Bursey, 2008;Olivares et al., 2009) that allows the interpretation of the collected spectra and associate specific peaks with minerals.

| Maltese chert sources
The chert samples of Malta present spectra with peaks that relate predominantly to silicate and carbonate minerals. The main peak in most of the spectra falls within 1,098 and 1,100 cm −1 , which relate to the opal-A mineral ( Figure 6). An additional smaller peak (about 472 cm −1 ) is also associated with this type of mineral. These findings suggest that opal-A is the predominant mineral of these chert outcrops. Secondary peaks (e.g., 1,632, 789 cm −1 ) are recorded in most of the samples that signify the presence of tridymite minerals. There is one sample (F1S2) that has the principal peak (1,104 cm −1 ) in the absorbance bands of tridymite minerals (Figure 6b). Quartz has been   imported to indicate that the values of an element had RSD and %REC outside the accepted values (RSD < 5 and 95% < %REC < 105%). BDL (below detection limit) signifies a value for oxides or elements where the concentration is below the measured limit. Lastly, the FTIR examination records some minor peaks (e.g., 2,003 cm −1 ) which have not been connected with specific minerals.
The chert samples of Gozo also present spectra with peaks related to silicate and carbonate minerals. The main peak (e.g., 1,098 cm −1 ) is found within the absorbance bands of the opal-A mineral (Figure 7).
This, in addition to two smaller peaks (e.g., 1,637, 472 cm −1 ) confirms the dominance of opal-A minerals in these chert samples. Tridymite is reported (Figure 7b), but only with one characteristic secondary peak (about 789 cm −1 ). The FTIR spectrum of only one sample (i.e., G2S6) presents peaks (i.e., 1,879, 695 cm −1 ) characteristic of quartz minerals The only exception is one chert sample (i.e., G2S6), which shows a total absence of carbonate minerals (Figure 7a).

| Skorba chert assemblages (SKB)
The samples from this assemblage predominantly present spectra with peaks within the absorbance bands of tridymite and calcite.
They could be the dominant mineral of the samples, but they are mainly secondary minerals. Tridymite is identified with two characteristics peaks (e.g., 785 and 668 cm −1 ) and calcite with three (e.g., 1,429, 875 and 713 cm −1 ). Some samples (e.g., SKB16/ L6/S13) have the main peak with values close to 1,080 cm −1 (±4 cm −1 ) which is characteristic of quartz (Figure 8a). Another characteristic feature of these spectra is the two adjacent peaks that support the predominance of quartz. One peak falls within the absorbance bands of 777 and 780 cm −1 , while the second is between 795 and 798 cm −1 (Figure 8a). These samples also present peaks within absorbance bands associated with flint (e.g., 1,163 and 557 cm −1 ), which is a silicate rock mainly consisted of quartz minerals (Boggs, 2009).
Some other samples (e.g., SKB16/S3/L30) present their main peak (i.e., 1,070 cm −1 ) and a minor (i.e., 460 cm −1 ) within the restricted bands of the opal-A mineral (Figure 8b). This assemblage, however, presents many samples with mixed results and makes it difficult to derive conclusive identifications of their silicate minerals.
Their main peak (e.g., 1,074 cm −1 ) is on the borderline between the opal-A and the tridymite minerals. Moreover, most of these samples present at least one of the characteristic peaks (i.e., 785 and

| First remarks
The show which elements should be selected for such research on chert (e.g., Al, Fe, REE). Moreover, the selection of these elements is made based on the extent that these factors influence their concentration and therefore place the examined rocks in specific categories (Chatzimpaloglou, 2019). The elementary composition of the samples and the subsequent ratios are shown in Tables 3 and 4.

| Chert sources
The work of Junguo, Yongzhang, and Hongzhong (2011)  The employed model uses the ratio Fe/Ti and Al/(Al + Fe) to distinguish between three characteristic depositional environments (Murray, 1994). This model (Figure 9b) demonstrates again that all of the Maltese cherts are plotted in a region related to a pelagic and continental margin environment.
Further research on the geochemistry of cherts (e.g., Kemkin & Kemkina, 2015;Malyk-Selivanova et al., 1998;Masuda, 1977;Murray et al., 1992;Owen et al., 1999) has shown that the relative fractionations of the REEs 2 are a good geochemical tracer for studying the chert rocks (Murray et al., 1992). In comparison with the major and trace elements, the REEs are not affected by the age of the rock or the tectonic history and are independent of diagenetic modification (Murray et al., 1992). These studies promote normalised patterns that allow a holistic perspective of their concentration and the relationship between them. The values of the REEs are always normalised with suitable rock standards to avoid unnormal fluctuation of elemental abundances. The World Average Shale standard (Piper, 1974) has been selected as the most appropriate for this study (Chatzimpaloglou, 2019).
The patterns of the Maltese samples are almost identical to each other with only some minor differences ( Figure 10). These samples have low concentrations (10 −1 ) of these elements and present a noticeable depletion of Tb and minor depletion of Ce, always in comparison with the neighbouring elements.

| Skorba chert assemblages (SKB)
The geochemical investigation of the chert artefacts follows the theoretical background presented above. The majority of the F I G U R E 8 Representative ATR spectra of the artefact samples from Skorba. Quartz is represented in these spectra with peaks around 1,080 cm −1 . Opal-A is represented in these spectra with peak around 1,070, 786 and 460 cm −1 . Calcite is represented in these spectra with peak between 1,410-30 Having the local source as reference material, they were divided into two big groups. The first group includes artefacts with macroscopic similarities to the Maltese chert, while second includes those that are highly unlikely to be related to them.

| First group of artefacts (local chert artefacts)
The members of this group are mainly opaque, dull and spotted artefacts ( Figure 13), which are characteristic of the local chert sources. The latter feature (i.e., spotted) especially is the trademark of the Maltese cherts because the examination has recorded that these irregular, white spots are actually the carbonate fossils found in these rocks (Chatzimpaloglou, 2019). They consistently appear on both the artefacts and the local chert sources, and provide the key macroscopic evidence that connects these artefacts with the Maltese cherts. An additional common feature is their colour, which varies between grey (e.g., 5Y 6/1) and brown shades (e.g., 10YR 6/6). The These are actually the same as the ones obtained from the Maltese chert source/outcrops. This is better illustrated in the comparable spider plots, which include samples of the Maltese outcrops and the assemblage (Figure 16a). Furthermore, the compatibility of artefacts from the different contexts of Skorba suggests a consistent usage of the local sources throughout the occupation/activity of this archaeological site (Figure 16b).
This group does not include artefacts that have similar features with the unique outcrop in Gozo. The results collected from these samples are contradictory, and it was decided that these should be included in the second group and their affiliation tested separately.

| Second group of artefacts (imported chert artefacts)
This group of chert artefacts includes predominantly small (L and W < 2.5 cm), homogeneous, shiny, fine-grained and highly translucent material. However, the significant diversity of colours and the different level of translucency makes this group heterogeneous. Indeed, the macroscopic examination has recorded many single artefacts with different characteristics from all the other members. They are all under the umbrella of the four features stated above, but these are insufficient to make any suggestions about their origin. Common macroscopic characteristics are useful for initial remarks but cannot be solely relied upon to suggest a common source.
Nevertheless, these remarks are supported by the results of the FTIR-ATR, which showed that all the artefact samples consisted mainly of quartz. These findings appear to exclude the Maltese chert from the list of possible sources, and the focus should, therefore, fall on nonlocal sources. This recommendation has been tested and recent research has already shown that some of these finds originated from Sicilian cherts (Chatzimpaloglou et al., 2020). However, there are other artefacts with conflicting findings and more research is necessary to be able to firmly suggest their origin.
This is the situation with three white, shiny, translucent, fine- materials. The geologically grounded and scientific approach, presented in this paper, is more than capable of providing strong evidence for this type of investigation.

| Methodological remarks
The methodology employed is based on geological and petrological techniques suitable for identifying different aspects of a rock formation. Although these are not related to conventional archaeological research, they are more suitably used to source lithic materials. The techniques used in this study have found strong and interpreted based on specific geochemical and geological theories (Luedtke, 1992;Murray, 1994). For example, the normalised value of Ce has been used to distinguish the chert rocks based on their depositional environment. Previous geochemical research (e.g., Kemkin & Kemkina, 2015;Masuda, 1977;Murray, 1994;Owen et al., 1999) testing this factor has provided the theoretical background, shown its significance and the expected range of values.
Nonetheless, many provenance studies use multivariate statistical analysis without connecting them with the necessary geological background. They do not explain the geochemical theory that led to the selection of the measured elements nor do they provide a geochemical/geological justification of their statistical results.
F I G U R E 1 9 Geochemical models cross-examining the Gozitan white chert and the artefacts of the second group. (a) Ternary diagram examining the type of the sediments and (b) binary diagram examining the type of depositional environment of the artefact samples. The line demarcations have followed the suggestion of the literature (Junguo et al., 2011;Murray, 1994)  This, however, should not be regarded as a total rejection of research focusing on multistage statistical data assessments. There has been important work, especially using trace elements, which has contributed to chert sourcing investigations (e.g., Malyk-Selivanova et al., 1998;Moreau et al., 2016;Roll et al., 2005). They generally rely on elements (e.g., Al, Fe and Sr) that either have been proven stable The next subject of discussion and always a debatable issue in such investigations is the selection of the best techniques to use in provenance investigations. There is no right answer to this, as there are always going to be issues of availability and funding, which cannot be underestimated. The main concern must be to select a group of techniques that provides the necessary types of results to reach the goals of the research. The types of results that every researcher needs to investigate are the macroscopic, mineralogical and elementary contexts of the lithic samples. The first should follow the baseline provided by previous researchers (Crandell, 2006;Luedtke, 1992) on sourcing lithics to minimise the subjective element that it is always present in such investigations. Systematic macroscopic investigation allows the scientific grouping of the artefacts and minimises the effort required for selecting representative samples.
Nonetheless, it is a subjective technique and lacks the validation to connect lithics with their sources alone.
The mineralogy of rocks is indicative of their formation process and can provide evidence of the different type of rock material.
There are rock materials, such as chert, which are considered homogeneous and dominated by one single mineral. However, this study has revealed the significant mineralogical differences between the cherts of Malta and some chert artefacts of Skorba, which highlights the importance of assessing this factor. There are many techniques that can provide this information, but in this study, FTIR-ATR spectroscopy was used. It is the best and the less invasive method (less than 10 μg sample is required) to record with great accuracy the mineralogical context of the samples. Although it is an invasive technique, it is far less destructive than microscopy that requires the preparation of thin sections. It does not give information about the fossils or the internal structure of the source, but rarely is such information necessary for sourcing lithics.
Similar results can be obtained by using the X-ray diffraction technique and it is more accurate than the FTIR-ATR. The disadvantage of this technique is the requirement of powder samples of 2 g and more in size, which is a significant quantity when removed from archaeological artefacts.  (Speer, 2014). The concentrations of the elements are used in wellexplored models to identify important aspects of the rock samples (Brandl et al., 2018;Morgenstein, 2006;Roll et al., 2005). Although such information is strictly geological, it is suggested that only materials from the same source can present similar results in specific categories (Murray, 1994;Murray et al., 1992). CHATZIMPALOGLOU | 917 XRF has been a very popular technique used for sourcing lithics and particularly in the Mediterranean region. It is a fast and nondestructive technique, yet a qualitative method with limited applications (Kempe & Harvey, 1983;Luedtke, 1992). It is very useful in the field for the quick separation of materials and when access is limited, but it is not suitable for homogeneous material, such as chert rocks. Moreover, the analysis is conducted on the surface of the samples, which occasionally produces results that can be easily misinterpreted and lead to the wrong conclusions. In addition, it is considered unreliable when the research is focusing on light elements such as Si.
Many geological research and sourcing studies have used neutron activation analysis (NAA) as an alternative method to record the geochemical composition of samples (Luedtke, 1978;Lyons, Glascock, & Mehringer, 2003). However, this requires a Neutron activation reactor which is something not commonly found in research laboratories. On the contrary, most of the earth science laboratories and departments have an ICP-MS (or equivalent) that solves paperwork and administration problems. In addition, NAA is much more costly and time-consuming than the ICP-MS technique.
Moreover, the recent addition of LA has minimised the effect on the samples (powder samples are needed for ICP-MS) and actually to a lesser extent than using FTIR-ATR. Furthermore, it allows the analysis of many samples within a "one run" process, which has significantly reduced the cost of using this technique.
This though has an impact on the accuracy of the collected results in comparison with the traditional bulk ICP-MS analyses.
The powder samples can provide more reliable results on the actual concentration of each element than from spot analyses.
Although the accuracy of an LA-ICP-MS has been exhaustively tested, it is advisable to use ratios between elements and not their Some investigations (Gale, 1981;Delage, 2003)  The potential of this methodology has been tested on Neolithic chert artefacts from the archaeological site of Skorba on Malta. The findings of this case study show that many of these artefacts originated from the local chert resources. Furthermore, the study distinguishes specific artefacts and provided strong evidence that they are of nonlocal origin.
This paper suggests a holistic methodological approach which is capable of addressing the provenance of chert archaeological finds worldwide. An additional aim of this study is to initiate a discussion for optimising this sourcing methodology, which should make a significant contribution to future archaeological research and practices. author would like to thank the anonymous reviewers for their constructive comments that improve the original manuscript.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available from the corresponding author upon reasonable request.