Handheld X-ray Fluorescence Spectrometer Research Articles

What jewelry did people wear in the Middle Byzantine period (10th-12th C. CE) in the Peloponnese? A technological and analytical case study

The present paper presents the preliminary results of the archaeometric analysis of a Middle Byzantine jewelry assemblage made of non-precious metals from the ancient site of Pallantion, near Tripoli (Peloponnese, Greece). The assemblage under examination consists of 26 artifacts, including earrings, finger rings and buckles. Macroscopic observations and optical microscopy were used to examine the manufacturing technology of the artifacts, with a particular focus on the manufacturing technology of wires. The proposed methodology combined a Handheld X-ray Fluorescence Spectrometer (HH-XRF) and a Micro X-ray Fluorescence Spectrometer (μ-XRF) to group the alloys used in the manufacture of the jewelry, despite the presence of corrosion. This methodology indicated that the majority of the artifacts was made of bronze, leaded or not, and gunmetal. Moreover, a quantification criterion was used to determine the state of preservation of the surface of the jewelry. Overall, the present study highlights the manufacturing technology of jewelry of the Middle Byzantine period and the tendency to imitate silver jewelry with lower-cost materials.

Technical note: Application of Handheld X-ray fluorescence spectrometers in forensic analysis of cigarette ash

Cigarettes are part of a collection of objects found everywhere and smoked by a large part of the population. Cigarette butts can be an essential piece of evidence in identifying a certain suspect/witness, as they can suggest the positive identification or exclusion of one or more brands by comparison or even DNA analysis. The main objective of this study is to test the capability of Handheld X-ray fluorescence spectrometer (HHXRF) to analyze the elemental concentration of individual cigarette ash of several tobacco brands and investigate if it is further possible to discriminate the different brands based on their ash’s elemental concentration. This study reveals the capability of HHXRF to discriminate tobacco brands based on their ashes' elemental concentration, with the great advantage of the analyses being non-destructive and can be carried out on a small sample. In addition, this equipment can measure the ash's elemental concentrations on-site, allowing for less contamination and sample loss.

Handheld XRF in ceramic research: a case study from the Lower Guadalquivir region

Handheld X-ray fluorescence spectrometer in the last 15 years become very popular and nowadays is a wellestablished device in archaeometry. This paper presents reflections based on the practice of using a spectrometer over the last years, trying to highlight both the advantages and disadvantages of this tool. To illustrate the potential of the device for research on more general than technical issues in archaeology, the results of spectroscopic analyses from two, closely located archaeological sites in western Andalusia, Setefilla necropolis and Setefilla settlement, is presented. Thanks to the potassium-titanium test it can be noticed that the results vary for each site, and the differences in elemental composition are interpreted as manifestations of the intentional use of different paste recipes for specific social practices.

Precise in-situ detection of inorganic pigments in ancient architectural color paintings by HH-XRF

The handheld X-ray fluorescence spectrometer (HH-XRF) is commonly used to detect the inorganic elemental composition of pigments on-site. However, the accuracy of in-situ detection results can be affected by the characteristics of the painted surface contaminants and the layered structure of pigments in ancient architectural color paintings. To mitigate this error, a method was proposed that combined the XRF spectra of inorganic pigments with the elemental concentration values obtained through principal component analysis (PCA). Additionally, this study discussed the typical surface contaminants and pigment layering found in color paintings separately. Firstly, experiments were conducted on dust accumulation layers of varying thicknesses. The results indicated that the condition of color paintings after pretreatment of dust accumulation tended to resemble the situation with thin dust accumulation during in-situ testing. A fitting formula was derived to establish a relationship between field testing and laboratory testing results. Secondly, experiments were conducted using various combinations of pigment layers. Based on the findings, it was hypothesized that there was a connection between XRF detection results and the maximum concentration value of a single element (as determined by XRF, in an unmixed or unlayered pigment sample without dust or smoke accumulation). The test results were fitted using a Polynomial formula, providing evidence for the existence of a nonlinear functional relationship between these two variables. Finally, an empirical formula for predicting the concentration values of the top color layer with different base colors was proposed. This study offered a precise method for accurately assessing pigments of ancient architectural color paintings through in-situ testing.

GEOLOGY AND HXRF GEOCHEMISTRY OF METAMORPHIC XENOLITHS IN TOWN MOUNTAIN GRANITE AT “THE SLAB” SWIMMING HOLE, LLANO UPLIFT, KINGSLAND, TEXAS

Abstract Metamorphic xenoliths in the Town Mountain Granite are exposed at “The Slab,” a low-water crossing in Kingsland, Texas, that is popular both for recreation and as a stop on regional geology field trips to the Llano uplift. Difficulty in sampling the pavement-style outcrops limits observation and analysis to that which can be completed at the outcrop. We use structural orientation measurements and a handheld X-ray fluorescence spectrometer (hXRF) to study xenolith orientation in context of regional fabrics, assess evidence of xenolith assimilation into the Town Mountain Granite, and investigate the origin of the xenoliths based on bulk composition. A nearly 1:1 correlation between the orientations of the xenoliths’ long axes and their internal foliation suggests that granite intrusion along foliation strongly controlled the xenoliths’ shapes. The orientation of the xenoliths’ foliation is consistent with dominant regional foliations. The hXRF analyses are able to discriminate between the compositions of the granite and the xenoliths. Xenolith compositions are consistent with a mafic protolith and suggest they have the same or similar sources; different analytical techniques for previously published bulk compositional analyses prevent direct comparison with our data or confident identification of a source unit. Limited assimilation of the xenoliths into the granite is suggested by magma injections into xenoliths, mafic residue from partial melting, chemical gradations at contacts between the granite and xenoliths, and possible enrichment of xenoliths in FeO + MgO relative to bulk compositions of the metamorphic country rock. These results encourage future use of hXRF for outcrop-based geological studies.

Comparison between Acid Digestion (ICP-OES) and X-ray Fluorescence (XRF) Spectrometry for Zinc Concentration Determination in Rice (Oryza sativa L.).

The determination of mineral concentrations in rice grain samples is crucial for analyzing their nutritional content. Most mineral content analysis techniques depend on inductively coupled plasma (ICP) spectrometry and are often complicated, expensive, time-consuming, and laborious. Recently, the handheld X-ray fluorescence (XRF) spectrometer has been randomly used in earth sciences; however, it is hardly practiced in quantifying mineral content in rice samples. In this research, the reliability of XRF results was compared with that of the ICP-OES to determine zinc (Zn) concentration in rice (Oryza sativa L.). Approximately 200 dehusked rice samples and four known high-Zn samples were analyzed using both XRF and ICP-OES techniques. The concentrations of Zn were recorded using the XRF technique and then correlated with the ICP-OES results. The results indicated a high positive relationship between two methods, with R2 = 0.83, p = 0.000, and the Pearson correlation value of 0.91 at the level of 0.05. This work demonstrates the potential of XRF as a reliable and low-cost as well as an alternative technique to ICP-OES methods for determining Zn content in rice as it allows the analysis of a greater number of samples in a short period at a considerably low price.

Examination of Metal Finds from the 10th Century Cemetery of Kiskunfélegyháza (Hungary)

This case study presents the results and conclusions of chemical and metallographic analyses carried out on metal finds (gilded silver mounts, jewelry made of silver- and copper-based alloys, and iron horse fittings) found in nine graves excavated at the 10th century site of the Terjék-tanya at Kiskunfélegyháza (Hungary). The examinations were performed with portable handheld X-ray fluorescence spectrometer (ED-XRF), optical microscopy (OM) and scanning electron microscopy equipped with an energy dispersive spectroscope (SEM-EDS). Beside the determination of the chemical composition of the non-ferrous artefacts and the inclusions of the iron samples, the aim of the study was to detect traces and characteristics of different manufacturing methods such as fire gilding, forging, etc.

Application of a handheld X-ray fluorescence analyzer for the quantification of air particulate matter on Teflon filters

Elemental characterization of air particulate matter samples through the application of X-ray fluorescence (XRF) spectrometry is a widespread analytical technique. This work presents the optimization and calibration methodology of a handheld XRF spectrometer and its subsequent application in elemental quantification of unknown particulate matter samples. The optimization of the handheld spectrometer was conducted through investigation of the elemental sensitivities and Limits of Detection (LoD) at variable excitation conditions (voltage, filter). Accordingly, five optimum operating conditions were obtained each one targeted in different elemental range: 1) Z = 11–12, 2) 12 < Z < 17, 3) 16 < Z < 23, 4) 22 < Z < 31 and 5) 30 < Z < 92. Subsequently, a number of reference (5 multi-element and 42 compound/single-element) materials were used to obtain calibration curves for 24 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Pb). Weighted least-square regression analysis was implemented to best fit the experimentally measured intensities with mass loadings resulting for most of the elements to high correlations (Pearson r > 0.98) and low statistical error. In addition, intercomparison of the elemental concentrations from 28 unknown particulate matter samples between the handheld and a benchtop XRF spectrometer showed good agreement.

Comparison of X-ray Fluorescence (XRF) and Atomic Absorption Spectrometry (AAS) Results for an Environmental Assessment at a Mercury Site in Kyrgyzstan

Khaidarkan, Batken Province, Kyrgyzstan is home to one of the world’s largest and last primary mercury mines. Doctors without Borders (MSF) and the Ministry of Health (MOH) of Kyrgyzstan have found that the Batken region has an elevated rate of non-communicable diseases (NCD) within the country. NCD can be caused by environmental pollution. A human health risk assessment was conducted to investigate heavy metal exposure. Using a hand-held X-ray fluorescence (XRF) spectrometer for soil screening is faster and less expensive than reliance on bench-scale methods. To establish a site-specific mercury conversion factor between XRF and the local MOH lab’s Atomic Absorption Spectrometry (AAS) with a Pyrolyzer attachment, soil samples were collected in Khaidarkan and surrounding villages. Samples were analyzed by XRF in three stages: in situ, ex situ-bulk, and ex situ-sieved. The ex situ-sieved samples were analyzed by AAS. Analysis results indicate that in situ readings can be used as a qualitative tool for screening, and a conversion factor of 1.7 was most appropriate for converting ex situ-bulk/ex situ-sieved and AAS results. This analysis enables the MOH laboratory and others to use XRF as a quick and cost-effective monitoring tool for Hg contamination in soil.

Portable X-ray fluorescence (pXRF) calibration for analysis of nutrient concentrations and trace element contaminants in fertilisers

With the increasing popularity of local blending of fertilisers, the fertiliser industry faces issues regarding quality control and fertiliser adulteration. Another problem is the contamination of fertilisers with trace elements that have been shown to subsequently accumulate in the soil and be taken up by plants, posing a danger to the environment and human health. Conventional characterisation methods necessary to ensure the quality of fertilisers and to comply with local regulations are costly, time consuming and sometimes not even accessible. Alternatively, using a wide range of unamended and intentionally amended fertilisers this study developed empirical calibrations for a portable handheld X-ray fluorescence (pXRF) spectrometer, determined the reliability for estimating the macro and micro nutrients and evaluated the use of the pXRF for the high-throughput detection of trace element contaminants in fertilisers. The models developed using pXRF for Mg, P, S, K, Ca, Mn, Fe, Zn and Mo had R2 values greater or equal to 0.97. These models also performed well on validation, with R2 values greater or equal to 0.97 (except for Fe, R2val = 0.55) and slope values ranging from 0.81 to 1.44. A second set of models were developed with a focus on trace elements in amended fertilisers. The R2 values of calibration for Co, Ni, As, Se, Cd and Pb were greater than or equal to 0.80. At concentrations up to 1000 mg kg-1, good validation statistics were also obtained; R2 values ranged from 0.97–0.99, except in one instance. The regression coefficients of the validation also had good prediction in the range of 0–100 mg kg-1 (R2 values were from 0.78–0.99), but not as well at lower concentrations up to 20 mg kg-1 (R2 values ranged from 0.10–0.99), especially for Cd. This study has demonstrated that pXRF can measure several major (P, Ca) and micro (Mn, Fe, Cu) nutrients, as well as trace elements and potential contaminants (Cr, Ni, As) in fertilisers with high accuracy and precision. The results obtained in this study is good, especially considering that loose powders were scanned for a maximum of 90 seconds without the use of a vacuum pump.

New results on horse trappings from the Hunnic-period Carpathian Basin based on non-destructive archaeometric analyses

Objects manufactured from pressed gold, gilded silver or copper alloy plates are characteristic assemblages from the Late Hunnic period (5th century AD, 420/430). In this study, horse trappings that belong to the ‘pressed gold plate horizon’ from three archaeological sites in the Carpathian Basin (Léva, Nyíregyháza-Oros and Pécsüszög) were analysed non-destructively by using a handheld X-ray fluorescence spectrometer. The main aims were to determine the chemical composition and the gilding technique used, and to attempt to prove whether the groups in an assemblage are from the same set. The results of the chemical analyses give us the opportunity to confirm whether damaged or presumably lost objects of an assemblage were replaced or repaired. According to the results obtained, the objects were manufactured from gold (Pécsüszög), gilded silver (Nyíregyháza-Oros) or gilded unalloyed copper plates (Léva). Later, replacements can be distinguished based on their chemical composition and manufacturing quality. Two types of gilding were observed: fire gilding with the presence of mercury (Léva), and leaf gilding (Nyíregyháza- Oros).

XRF elemental analysis of inks in South American manuscripts from 1779 to 1825

The Regional Archive of Cusco in Peru guards valuable history collections with exceptional regional and international value dating from the sixteenth century to the present. Historical manuscripts are part of the identity of all people; they constitute a tangible cultural heritage that must be studied, valued, and protected. In this sense, the objective of this research was to identify the chemical compositions of inks and paper, with the goals of setting the background of their originality, identifying relationships between them, and glimpsing antecedents that generated degradation due to the compositions of the inks. This study is the first of its kind in Peru and reveals the chemical elements present in the writing ink, the seal, and the paper of five documents from the late eighteenth and early nineteenth centuries. Duplicate in situ nondestructive analyses were carried out using a hand-held X-ray fluorescence spectrometer under ambient conditions in soil mode, configured with three sequential shots, and energies from zero to 40, 40, and 15 keV, respectively. The elements S and Fe were present as components of iron gall inks. Cu and Zn were less abundant; probably, they provided less corrosion and more color intensity to the inks. The minor elements Pb, As, and especially Ag in all manuscripts differentiate them from European inks of the same period. Additionally, the five documents reflect the same elemental compositions but with different concentrations. This could mean that writers used local raw materials and Spanish ink recipes. Finally, the analyses of standard reference material, SRM 1646a and SRM 196b, gave results with acceptable precision.Graphical

Determination of Nutrients in Liquid Manures and Biogas Digestates by Portable Energy-Dispersive X-ray Fluorescence Spectrometry

Knowing the exact nutrient composition of organic fertilizers is a prerequisite for their appropriate application to improve yield and to avoid environmental pollution by over-fertilization. Traditional standard chemical analysis is cost and time-consuming and thus it is unsuitable for a rapid analysis before manure application. As a possible alternative, a handheld X-ray fluorescence (XRF) spectrometer was tested to enable a fast, simultaneous, and on-site analysis of several elements. A set of 62 liquid pig and cattle manures as well as biogas digestates were collected, intensively homogenized and analysed for the macro plant nutrients phosphorus, potassium, magnesium, calcium, and sulphur as well as the micro nutrients manganese, iron, copper, and zinc using the standard lab procedure. The effect of four different sample preparation steps (original, dried, filtered, and dried filter residues) on XRF measurement accuracy was examined. Therefore, XRF results were correlated with values of the reference analysis. The best R2s for each element ranged from 0.64 to 0.92. Comparing the four preparation steps, XRF results for dried samples showed good correlations (0.64 and 0.86) for all elements. XRF measurements using dried filter residues showed also good correlations with R2s between 0.65 and 0.91 except for P, Mg, and Ca. In contrast, correlation analysis for liquid samples (original and filtered) resulted in lower R2s from 0.02 to 0.68, except for K (0.83 and 0.87, respectively). Based on these results, it can be concluded that handheld XRF is a promising measuring system for element analysis in manures and digestates.

Monte Carlo simulation for the analysis of various solid samples using handheld X-ray fluorescence spectrometer and evaluation of the effect by environmental interferences

Handheld X-ray fluorescence (HH-XRF) has expanded its utilization areas according to recent technological developments. Most current applications, though, are still concentrated in traditional areas including mineral resource analysis and environmental regulation rather than forensic science for the purpose of investigating a nuclear security event involving nuclear material out of regulatory control. To apply HH-XRF to nuclear material analysis, it is necessary to first obtain calibration data using standard reference materials. Considering the difficulty in obtaining such standard reference materials as well as the high costs involved, one well-known alternative method is to use Monte Carlo simulation code. This study investigated the feasibility of employing Monte Carlo N-Particle transport 6 (MCNP6) simulation to provide calibration data through comparison with experimental measurements of pure solid samples of graphite, copper, SiO2, and UO2 using HH-XRF. The results showed that the MCNP6 simulation results were entirely consistent with the measurement spectra, except for environmental interferences stemming from interactions with the mechanical components below 10 keV which varied slightly according to sample type. To quantitatively evaluate the effect of these environmental interferences on the whole spectrum, the coefficient of determination (R2) was used. In the case of graphite, the effect of the environmental interferences was evaluated to be about 20% on the conformity of the measured and simulated results, while those for copper, SiO2, and UO2 were about 1%, 3%, and less than 1%, respectively. These results indicate that samples having elements with higher rates of photoelectric absorption followed by fluorescence compared to scattering tend to decrease the effect of the environmental interferences over the entire spectrum. The origin of the environmental interferences was estimated to be interference with the detector shield and/or X-ray tube collimator, which are particular design features of the device used. Their effect on contributing to the environmental interferences was evaluated by experiment for the detector shield and simulation for the X-ray tube collimator. As the detector shield was found to only contribute to a decrease in overall spectrum intensity, the major contributor to the environmental interferences was determined to be the collimator. It is believed that the results of this study will help to confirm that Monte Carlo simulation can properly provide calibration data for using HH-XRF on nuclear materials for which reference materials are hard to obtain.

A New Species of Argophyllum (Argophyllaceae) with Notes on the Species from New Caledonia and Nickel Hyperaccumulation.

The taxonomy of Argophyllum (Argophyllaceae) in New Caledonia is reviewed here. All names validly published in Argophyllum in this archipelago are discussed and lectotypified when necessary. A new species is described, Argophyllum riparium (The LSID for the name Argophyllum riparium is: 77216335-1) Pillon and Hequet sp. nov. Argophyllum grunowii and A. ellipticum are both species complexes in which several species previously recognized are included here as well. Seven species are recognized in New Caledonia: A. brevipetalum, A. ellipticum, A. grunowii, A. montanum, A. nitidum, A. riparium and A. vernicosum, all endemic. Leaf nickel content of A. riparium can exceed 1000 μg·g−1, which makes this species a nickel hyperaccumulator. Measurements with a handheld X-Ray Fluorescence (XRF) spectrometer confirmed that this was also the case for all other species from New Caledonia, except A. nitidum. An identification key of New Caledonian species is provided.

Thickness determination of the gilding on brass materials by XRF technique

The gold coating layer of the gold-plated brass objects was estimated using calibration curves obtained with a handheld X-ray fluorescence spectrometer (XRF). Calibration curves were obtained using reference materials (Au and brass) and intensity ratios of the X-ray fluorescence peaks generated in both the gold coating and the brass substrate. In addition, a calibration was also performed with the PLS (Partial Least Squares) multivariate analysis method. Good agreement was obtained by comparing the results of the different methods. The calibrations were successfully applied to gold-plated brass jewels and samples.

Blepharidium guatemalense, an obligate nickel hyperaccumulator plant from non-ultramafic soils in Mexico

Nickel hyperaccumulation in Blepharidium guatemalense Standl. (Rubiaceae) was found in the tropical forests of south-eastern Mexico. This study aimed to document the geographic extent of nickel hyperaccumulation in this species, to understand its process of hyperaccumulation and to explore nickel distribution within the tissues of this plant. To accomplish these objectives, a complete non-destructive elemental screening of herbarium specimens was performed with a hand-held X-ray fluorescence spectrometer. Besides, rhizosphere soils and plant tissues were collected in Mexico and analyzed for physical–chemical parameters. Finally, elemental distribution maps of nickel and other elements in plant tissues were obtained by X-ray fluorescence spectroscopy and microscopy. This study revealed that Blepharidium guatemalense is distributed throughout Chiapas, Tabasco and Campeche, reaching the maximum nickel concentration in leaves (4.3 wt%) followed by roots and seeds (2.0 wt%) and bark (1.8 wt%). Simultaneous hyperaccumulation of cobalt and nickel was found in 15% of the herbarium specimens. Blepharidium guatemalense has uncommon re-distribution mechanisms via phloem since this tissue is the highest nickel-enriched from all parts of the plant (from roots to leaves). A high total nickel (mean of 610 µg g−1) was found in rhizosphere soils even though no evidence of ophiolite emplacement in that area has been reported. Blepharidium guatemalense represents the first hypernickelophore (> 1 wt% Ni) to be reported as growing in soils that are neither ultramafic nor enriched by anthropogenic pollutants.

Method of rapid assessment of sulfide sulfur content in host rocks

The aim of the research is to assess the possibility of using the energy-dispersive X-ray fluorescence method directly at the stoping operation site. To meet this objective, a hand-held X-ray fluorescence spectrometer of the expert class of the NITON XL2 brand was selected. This will solve the problem of developing an express method for assessing the explosive and fire-hazardous properties of sulfur-containing or pyrite-containing ore. The development of the method is dictated by the need for operational control of the dust explosion hazard of sulfur-containing rocks and the assessment of their tendency to spontaneous combustion and also the possibility of making amendments to the development process of complex heterogeneous host rocks. Visual and optical control methods were used as an auxiliary method. In the process of developing the express method, both express analyses were carried out directly at the face bottom, and monolithic large-sized pieces of mined rock mass and also additional laboratory studies of previously studied samples of these rocks dispersed to a size of less than 100 microns were performed. The obtained results allowed to draw a number of conclusions about the expediency of using the X-ray fluorescence express method and suggest ways to use it directly in the stoping face.

Verifying the feasibility of using Hand-Held X-ray fluorescence spectrometer to analyze Linqing brick: evaluation of the influencing factors and assessing reliability

Linqing brick is quite popular in Chinese history. Currently, identifying the origin of Linqing brick is an important issue to be studied in the field of archeology and architectural history in China. Hand-Held X-ray fluorescence (HH-XRF) spectrometry enables the in situ determination of the main elements in Linqing brick in a rapid non-destructive manner. HH-XRF is important in identifying the origin of Linqing brick. However, HH-XRF could be influenced by certain factors and may be capable of measuring only the element contents of the surface for the bricks in situ. The present study aimed to verify the reliability of HH-XRF and to systematically evaluate the different factors influencing measurement precision and accuracy so that scientific advice could be provided regarding the usage of HH-XRF for this application. Four experiments were performed to determine the influencing factors and assess the reliability through cross-validation using inductively coupled plasma optical emission spectrometry (ICP-OES). Finally, the influence of the different studied factors was studied, and the reliability of HH-XRF was ensured. The facts to consider about the measurement time, cross validation, criteria to select points, treat surface and getting final data and how to avoid the effect of rain, while using this method, are provided.

Application of handheld X-ray fluorescence spectrometer for major element analysis and characterization of geological samples in Southern Thailand

The handheld X-ray fluorescence spectrometer (hXRF) was applied to major element analysis in the geological samples and the results were compared with the results of the wavelength dispersive X-ray fluorescence spectrometer (WDXRF). In addition, the analytical compositions were confirmed by X-ray diffractometer (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). In the case of pXRF analysis, eight geological reference materials were used to calibrate the analytical method and four known concentration samples were used to prove the method. In research, ten geological samples from Phuket province, Thailand were collected with different depths corresponding to O horizon (0-0.1 m), A horizon (0.1-0.3 m), B1 horizon (0.3-1.0 m), B2 horizon (1.0-2.0 m), C1 horizon (2.0-3.0 m), C2A horizon (3.0-5.0 m), C2B horizon (5.0-8.0 m), C3 horizon (8.0-12.0 m), D horizon (12.0-20.0 m) and RK horizon (> 20.0 m). The elemental analysis results showed that the pXRF results were matched well with that WDXRF results. The concentration range in ten samples were Si (18-22 wt%), Al (12-15 wt%), Fe (1-4 wt%), K (0.4-3.2 wt%) and Ti (0.2-0.4 wt%). The concentration of some elements such as Ca and Mg on those ten samples are low and they are unable to analysed by hXRF. The XRD patterns revealed that all samples consisted of quartz, kaolinite, halloysite, illite, vermiculite and biotite.