The Reynolds Cup competition, named after Bob Reynolds for his pioneering work in quantitative clay mineralogy and his great contributions to clay science, was established in 2000 by Douglas McCarty and Jan Srodon of ChevronTexaco and Dennis Eberl of the United States Geological Survey (USGS). Unlike other round-robin events that used well-ordered, high-symmetry phases (Madsen et al., 2001) or splits from natural samples with unknown mineral composition (Ottner et al., 2000), the Reynolds Cup competition utilizes mixtures of pure standards that represent realistic sedimentary rock compositions. The first RC competition opened early 2002 and samples were made available to individuals in commercial, industrial, government, or academic laboratories, which could use any method or a combination of methods to obtain the most accurate quantitative phase analysis. Three samples each were given to a total of 40 participants. The TOP-3-finishers were presented with plaques and the champion’s trophy went to the first-place finisher. The competition was sponsored by ChevronTexaco and the trophy was donated by the USGS. The success of this competition encouraged the founders to make it a biennial event. The Reynolds Cup competition is now funded by the Clay Minerals Society CMS and the German-Austrian-Swiss Clay Group DTTG. The competition is free for all to enter. However, those that are not members of the CMS are encouraged (but not obliged) to become members.
The primary goal of the Reynolds Cup is to stimulate improvements in analytical techniques and individual skills. The CMS and the organizers of the Reynolds Cup offer this as a service to the scientific community, and depend on the good will and fairness of all involved. The selection of the winners during each competition by the Reynolds Cup Committee of the CMS is final.
The competition is held on a biennial basis and the process is facilitated by a committee set up by the CMS. Two years prior to the competition, the committee chooses a Principal Organizer who is responsible for preparing the mineral mixtures and conducting and judging the competition. So far, the winner of the immediate past competition has volunteered to organize the next event. Should the winner be unable to organize the competition, prior organizers would be willing to continue with arranging the event. Specific guidelines are described below:
The actual sample make-up is left to the discretion of the organizer, within the following guidelines:
Samples should be artificial clay-bearing rock mixtures representative of minerals usually found in natural sedimentary rocks or soils. The information about the represented rock type/environment will be provided with the samples.
High-purity minerals should be obtained from private and public collections
Samples should be prepared such that the purity of the minerals used in the mixture is known within 1 wt%.
A repeatable sample splitting procedure should be used and splits should be verified for consistency using XRD and XRF prior to sample distribution.
SOME KEY RECOMMENDATIONS FOR SUCCESS IN QUANTITATIVE ANALYSIS OF SAMPLES CONTAINING CLAY MINERALS
Experience has shown that X-ray powder diffraction (XRPD) is the best primary method for quantitative analysis of clay bearing samples. The following recommendations assume XRPD is the primary method employed, although the Reynolds Cup allows for any method(s) to be used.
There are three key recommendations:
1) Correct qualitative analysis i.e. mineral identification is a critical prerequisite to quantitative analysis. Therefore DO NOT rely solely on automated search/match routines. Misidentification of phases that are not present in the mixtures is THE biggest source of bias. Also, do not just rely on bulk sample analyses for mineral identification. Clay minerals in particular are more readily identified by separating clay size fractions (i.e. <2 µm) and applying diagnostic treatments and intercalation procedures, e.g. see Brown & Brindley (1980) and Moore & Reynolds (1997). Finally, do not just accept your identifications without some consideration of the sample type and system; is the assemblage of identified minerals realistic or are there more logical or common alternatives to be checked?
2) Quantitative analysis may be biased by numerous factors, so to avoid the most critical ones – ensure particle size is adequate (nominally < 10 μm) by wet grinding. Hand grinding alone is unlikely to achieve adequate particle size reduction. Try to avoid texture in your powder specimens, as preferred orientation effects are difficult to compensate for. Preferably, use full-pattern methods (e.g. Rietveld or experimental pattern summation) over single peak techniques for quantification.
3) Cross-check and validate your quantitative data where possible by independent measurements For example - Calculate the bulk chemical composition from your mineralogical analysis and compare with measured XRF or other chemical analysis data (any mineralogical analysis must be compatible with a chemical analysis) etc, etc.
Bish, D.L. and Reynolds, R.C., Jr. (1989) Sample preparation for X-ray diffraction. Pp. 73-99 in: Modern Powder Diffraction (D.L. Bish and J.E. Post, editors). Reviews in Mineralogy 20, Mineralogical Society of America, Washington, D.C.
Brown, G. and Brindley, G.W. (1980) X-ray diffraction procedures for clay mineral identification. Pp. 305-359 in: Crystal Structures of Clay Minerals and their X- ray Identification. (Brindley, G. W. and Brown, G. editors). Mineralogical Society Monograph No. 5, Mineralogical Society, London.
Moore, D.M. and Reynolds, R.C., Jr. (1997) X-ray diffraction and the identification and analysis of clay minerals, 2nd edition, Oxford University Press, New York.
The Reynolds Cup Committee organizes the biennial contests, defines general rules and scientific goals, supports the principal organizer, and reports to the CMS council. The committee is set up by the CMS. The first past president of the CMS will serve as an ex officio member. The winner (or leader of the winning group) of the immediate past RC will be the incoming chair for one year and the chair for the next two years. The membership after being the chair is on a volunteer principle. The number of committee members is restricted to six persons. If the number exceeds six members the one with the longest membership since winning will step back.
1. No qualitative information is given out. Therefore participants are expected to provide both qualitative and quantitative evaluations of all the samples.
2. All analytical methods are allowed for mineral identification and quantification but the use of routine methods applied in each participant's laboratory is encouraged.
3. A short description of the analytical procedure used must be reported together with the results.
4.Participants are encouraged to provide estimated errors of their analysis.
5. Participants are encouraged to report the phase composition in as much detail as possible even though minerals are grouped to streamline mineral names when judging. Extra information provided can be useful to break ties. The phyllosilicate/clay mineral phases will be evaluated in more detail. When returning results please use the provided spreadsheet indicating the minimum level to which the different types of (clay) minerals will be categorized for the purposes of judging: Reynolds_Cup_Contestant_Results_Spreadsheet.xls
6. Not less than one month prior to the CMS Annual Meeting , entries are to be returned to the organizer for evaluation and judging. The judging criteria are decided by the principal organizer based on the compositions of the pure mixtures. The entry with the smallest sum of absolute errors for the three samples provided will be the winner. In the event that several entries are within established uncertainties in the compositions of the pure mineral mixtures, the principal organizer liaises with the committee to impose stricter judging criteria to select the one winner, e.g. the total clay bias, the sum of relative errors, the number of non- or misidentified phases, and more specific (clay) mineral identifications.
7. After all the entries have been returned to the organizer, the true compositions of the samples and the mineral standards are made available to the participants.
8. Prior to the CMS meeting, participants are provided with an anonymous ranking of all the results.
9. Participants who do not wish to submit results are asked to return the intact samples to the principal organizer for redistribution.
10. Any use of additionally delivered sample material will exclude the participant from ranking.
11. Those who request samples and do not send in results or fail to return the samples unopened well before the due date will not be eligible to participate in future Reynolds Cups.
12. The top three finalists are announced at the CMS meeting and presented with commemorative plaques and the winner is presented with the Reynolds Cup. The cup is held by the winner until the next competition. The identities of the remaining contestants are kept confidential.
The winner was Reinhard Kleeberg of the University of Mining and Technology, Mineralogical Institute, Freiberg Germany. The second-placed finisher was Reiner Dohrmann of the Federal Institute for Geosciences and Natural Resources, Hannover, Germany. Tied for third-place were Denny Eberl of the USGS, Colorado and Stephen Hillier of the Macaulay Institute, Scotland.
The winner of the first Reynolds Cup, Reinhard Kleeberg, volunteered to organized the second Reynolds Cup competition in 2004. Funding for the second competition was primarily from the TU Bergakademie Freiberg, German Research Council, and IUCr CPD. The winner was Dipo Omotoso of Natural Resources Canada, orgon, Alberta. In second place was Douglas McCarty of Chevron, Houston, USA and tied for third were Stephen Hillier of the Macaulay Institute, Scotland and Michael Plotze of IGT Claylab, ETH Zurich, Switzerland. Results of the competition were published in the 2005 IUCr CPD newsletter 30.
The third RC competition was organized by Dipo Omotoso, winner of the second Reynolds Cup competition, with funding from Natural Resources Canada. Results of the contest were announced at the 2006 CMS/GFA annual meeting in Oleron, France. The winner of the contest was Douglas McCarty of Chevron, Texas, followed by Stephen Hillier of the Macaulay Institute, Scotland and Reinhard Kleeberg of TU Bergakademie, Freiberg, Germany. Details of the quantitative methods used by the top three finishers were published in the December 2006 edition of Clays and Clay Minerals. In addition to the commemorative plaques and trophy awarded to the top-placed finishers, the champion received $1000 towards travel expenses. Diffraction patterns and chemical composition of mineral standards used to prepare the 2006 contest samples may be obtained from Dipo Omotoso (email@example.com).
Fourth (2008) Reynolds Cup. The fourth Reynolds Cup was organized by the winner of Reynolds Cup III, Chevron, USA (Douglas McCarty) and Edwin Zeelmaekers (K.U.Leuven, Belgium) and saw 53 individual scientists or teams from 17 countries competing for the Cup. First place went to Steve Hillier (Macaulay Institute, Scotland) who won by a large margin. Oladipo Omotoso (CANMET, Canada) and Reinhard Kleeberg & Kristian Ufer (TU Bergakademie Freiberg, Germany) tied for second place. Four entries tied for third place: Katja Emmerich & Annett Steudel (University of Karlsruhe, Germany), Steve Chipera (Chesapeake Energy Corporation, USA), Dennis Eberl & Alex Blum (USGS Boulder, USA) and Mark Raven (CSIRO, Australia). All top-contenders were presented commemorative plaques and Steve Hillier received the coveted Reynolds Cup trophy. The Reynolds Cup will continue its tradition in 2010 and its 5th edition will be organized by the current winner Steve Hillier.
Steve Hillier is leader of the X-ray Diffraction section at The Macaulay Institute. He is a mineralogist by training with extensive experience and research publications in the field of quantitative analysis by X-ray powder diffraction. Clay minerals are his speciality but he also has a broad knowledge of the analysis of a diverse range of polycrystalline materials, including rocks soils, drillng muds, corrosion products and cements.
The 2010 - 5th Reynolds Cup recorded the best participation of any Reynolds Cup so far. Seventy-six sets of three samples were distributed and 63 participants from 22 different countries were brave enough to return results, 5 withdrew, and 8 failed to return. The first sample was meant to represent a clay-rich sediment from an evaporate environment; the second sample a clay that might be encountered in a hydrothermal alteration; and the third a clay-rich soil formed on a parent material rich in ferromagnesian minerals and amorphous soil minerals As such the analytical challenges were numerous. Furthermore, in contrast to previous Reynolds Cups the clay minerals/phyllosilicates were judged far more strictly by requiring participants to quantify to a greater level of detail in terms of clay mineral/phyllosilicate classification.
As with previous Reynolds Cups the blind round robin format affords participants an unrivaled opportunity to test their given methods in complete honesty and thereby identify both strengths and weaknesses. Each participant will receive a summary of the complete field of entries, with the identities of participants kept confidential. In addition summary information on the minerals used in the mixtures will also be distributed to participants. We hope that this feedback will help participants establish how they can improve their methods particularly when clay minerals are a major component.
So without further delay - we are pleased to announce that the 2010 5th Reynolds Cup ‘Champion’ is Mark Raven and Peter Self . Mark is the leader of the Mineralogical and Geochemical Services group at the CSIRO Land and Water, Adelaide, South Australia and has almost 30 years practical experience in XRD and XRF analysis. He undertakes research and orgelopment of methods of mineralogical analysis specialising in identification and quantification of minerals in rocks, soils and industrial materials.
Second place went to Denny Eberl and his team including Alex Blum, Mario Guzman , and missing from the photo Marc Serravezza and Keith Morrison , all working out of the USGS in Boulder, Colorado. Denny said "This was a great experience especially since we involved three students in our team all of whom worked hard, had fun and learned a lot".
Third place went to Reinhard Kleeberg and Kristian Ufer . Since 1987 Reinhard has been head of the "Mineralogical laboratory" of the Mineralogical Institute at the Technical University Bergakademie F reiberg and is a winner and organiser of previous Reynolds Cups. His team mate Kristian Ufer did his PhD working on the modelling of turbostratically disordered structures within the Rietveld method, as now used in several Rietveld codes, and was a recent recipient of the ‘Karl Jasmund Award’ of the German Clay Group (DTTG).
Just out of range of the top finishers and deserving an honourable mention for their 4th place was the Chevron entry by Edwin Zeelmaekers (currently at Shell) and Jan Srodon (Polish Academy of Sciences, Krakow). Reiner Dohrmann and Stephan Kaufhold , BGR/LBEG, Hannover, Germany earned 5th place.
Mark described his procedure as follows: ‘First I ran a preliminary back pressed XRD pattern of each sample without any grinding or any other preparation. 1.5g of each sample was then micronized under ethanol with a McCrone micronizing mill and oven dried at 60°C. The fine powders were back pressed and XRD patterns collected on a PANalytical X’Pert Pro MPD using iron filtered cobalt K alpha radiation. Patterns were collected from 3 to 80° 2-theta at 0.017° steps. Total data collection time was 30 minutes. The micronized samples were then calcium saturated twice with 1M CaCl2, washed with deionised water then ethanol (centrifuged at 6000rpm after each step) before oven drying at 60°C. XRD patterns were re-collected. 2g of the remaining samples were dispersed with 1M NaCl and centrifuged at various speeds to separate <0.2µm, 0.2-2µm and >2µm fractions. Pressed powders and oriented, magnesium saturated and glycerolated specimens were prepared to help identify the dominant clay species. Quantification was performed using SIROQUANT version 3 with modified HKL files prepared from several in-house clay standard materials. I think the most important step was probably having several standards to “calibrate” SIROQUANT HKL files. And a close second is calcium saturating the powders after micronizing.’
Denny said, ‘X-ray diffraction and the RockJock (RJ) computer program were the primary tools used to analyze the 2010 Reynolds Cup samples. The RJ program is an automated, whole-pattern fitting method by which a sample’s XRD pattern is modeled by summing patterns of pure mineral standards. The pure patterns are multiplied by factors that are varied by the Solver tool in Microsoft Excel until the degree of fit between the measured and the summed modeled pattern is minimized. Mineral percentages then are calculated from the integrated intensities of the pure patterns and of a corundum internal standard, and from previously measured reference intensity ratios (RIRs). Quantitative interpretations of X-ray diffraction patterns were based solely on randomly oriented, whole-rock samples. However, inclusion of the correct mineral standards is key in the RJ analysis, and mineral identification was supplemented by X-ray florescence (XRF) chemical analyses, and by qualitative mineral analyses using FTIR. In addition, clays were size separated from the samples, oriented on single crystal silicon wafers, and X-rayed to help constrain which clay standards should be used in the RJ analysis. Use of oriented clay mounts has become part of our routine quantitative mineral analysis of samples with complex clay content. We also found it helpful to run oriented XRD patterns of the whole rock for qualitative clay mineral identification, because some phyllosilicates were found mostly in the coarse size fraction of the RC samples.
One advantage to the whole pattern fitting method is that amorphous material can be analyzed. Amorphous material is expressed as humps in XRD patterns, but various amorphous materials have different shapes and different positions for these humps. In this manner, we could separate ferrihydrite from glass in sample three. A disadvantage to the RJ method is that one must have in RJ’s library all of the standards necessary to perform an analysis. When huntite turned up in one of the samples, we had to order this mineral from a supply house and enter its pattern and RIR into RJ.
Our second-place finish in 2010 is an improvement over a third place in 2008. Many improvements had been made to RJ during this interval. These modifications improved our ideal two-sigma relative error from ±12% to ±4%. The most important improvements are: (1) the use of corundum as an internal standard, rather than the zincite used previously, because zincite XRD peaks can broaden in response to grinding, especially in quartz-rich samples, leading to high totals; and (2) the use of a new method for achieving nearly perfectly random sample orientation that is more convenient to use than spray drying, previously the best method. The new method shakes (for 10 minutes) the previously ground sample plus corundum in a plastic vial with three plastic balls and a small quantity of vertrel (hexane works too). The sample then is sieved (250 micron), and side loaded into a sample holder. The advantages to this method over spray drying are that no sample is lost, no spray drier is required, and the sample does not tend to roll out of the sample holder.
For an unknown reason, the potassium test failed to reveal vermiculite in the third sample. Without this phase included in the RJ calculation, our total for this sample came to about 90%, which should have been a clue that a phase was missing. However, we are happy to finish second rather than in first place, for the obvious reason, and we thank Steve Hillier for the large amount of time and hard work that went into running the 2010 competition. Although we dedicated considerable time to analyzing the samples, it was time well spent because our analytical methods were improved’.
The RockJock program and instruction manual are available free at: ftp://brrcrftp.cr.usgs.gov/pub/ddeberl/
Reinhard and Kristian’s analysis began with an examination of the samples using optical microscopy and by size separation into >20 and <20 micron fractions, partly as aid to identification of phases. However, the original unfractionated samples along with the size fractions were all quantified by Rietveld refinement as a check on internal consistency. Some clay size fractions were also analyzed and formamide treatment was used to identify halloysite in RC5-2. SEM and EDS were used for supplemental identification and XRF and Ion Chromatography were used to constrain the maximum possible values for certain minerals such as barite and halite. The Reitveld program used was BGMNwin, with very careful selection of refined parameters and the application of a variety of models, some still very much in orgelopment, to describe various clays and phyllosilicates. Reinhard summarized the experience saying ‘we have learnt a lot and will use the samples to improve our models’.
Steve Hillier and Helen Pendlowski,
Macaulay Institute, Aberdeen, December 2010.
The 2012 - 6th Reynolds Cup continued on from the success of the 2010 contest with seventy-four sets of three samples distributed to participants from 25 countries. Fifty nine participants returned quantitative results, 3 returned qualitative results, 2 withdrew, 9 failed to return results and one participant’s samples went missing. Sample one was clay-rich sediment representing petroleum shales; sample 2 was clay-rich material representing a nickel bearing laterite; and sample three was clay-rich material representing minerals found in bauxite deposits. The analytical challenges were again numerous, including many minerals with overlapping XRD peaks and the presence of amorphous materials. Similar to the 2010 Reynolds Cup, clay minerals/phyllosilicates were judged more strictly by requiring participants to quantify to a greater level of detail in terms of clay mineral/phyllosilicate classification. It’s pleasing to see that many of the participants are updating their skills, which is evident by a significant reduction in the overall bias compared with the 2010 contest.
The Reynolds Cup round robin contest affords participants an unrivalled opportunity to test their proficiency in quantitative mineralogy. Each participant will receive a summary of the complete field of entries, with the identities of individual participants kept confidential. In addition summary information on the minerals used in the mixtures will also be distributed to participants. We hope this feedback will encourage participants to continually improve their methods particularly when clay minerals are a major component.
Therefore, we are pleased to announce that the 2012 6th Reynolds Cup ‘Champion’ is Michael Plötze, from Zurich, Switzerland.
Michael Plötze studied Mineralogy/Geochemistry at the Technical University Bergakademie Freiberg (Germany). Since 1998 he is employed at the ETH Zurich (Switzerland) and head of the ClayLab at the Institute for Geotechnical Engineering. His main research topics are the investigation of alteration of clay minerals and the modification of the physicochemical properties of clays during physical and chemical treatment as well as the initial soil/clay formation in weathering. The quantitative phase analysis of soils and rocks is of course one of the most important tools in his work.
Second place went to Steve Hillier, Helen Pendlowski and Ian Phillips from Aberdeen, Scotland.
Steve and his team from The James Hutton Institute, Aberdeen Scotland are no strangers to the Reynolds Cup, having placed in the top 3 in all but the 2010 contest in which they prepared the samples.
Third place went to Reinhard Kleeberg and Robert Möckel from Freiberg, Germany . Reinhard is also no stranger to the Reynolds Cup placing in the top 3 in all but the 2004 contest in which he prepared the samples. Since 1987 Reinhard has been head of the "Mineralogical laboratory" of the Mineralogical Institute at the Technical University Bergakademie, Freiberg, Germany. His team mate Robert Möckel is from the Helmholtz Institute, Freiberg Germany.
Falling just short of the top 3 finishers but deserving honourable mentions for their great efforts are; Youjin Deng from Texas A&M in 4th place, USA. In 5th place was the team of Kristian Ufer, Stephan Kaufhold and Reiner Dohrmann from BGR/LBEG, Hannover, Germany and in 6th place was Rieko Adriaens and Gilles Mertens: “KULeuven University Clay lab” and “Qmineral”, Heverlee, Belgium.
Congratulations to all our participants and particularly to our winners!
Michael described his procedure as follows:
1) Homogenization of the sample
2) Sample examination by optical microscopy and qualitative check for carbonates with HCl and magnetic minerals with a permanent magnet.
3) The tool used for quantification was only XRD and Rietveld refinement of XRD-patterns from randomly oriented specimens (front loaded with a blade). The Rietveld program used was AutoQuan (BGMN), with very careful selection of models and refined parameters (refinement range, background, real structure parameters).
3a) Micronizing of an aliquot of 1.5g of the whole sample in ethanol with a McCrone micronizing mill and oven drying at 60 °C.
3b) Collecting of X-ray pattern of randomly oriented specimen
3c) Adding Zincite (final content 20wt%) for quantification of amorphous content.
3d) Collecting of X-ray pattern of randomly oriented specimens XRD with CoKalpha, solid state detector, automatic divergence and antiscatter slit, 4° soller slits primary and secondary, 2-90°2Theta range, step size 0.02°2Theta, counting time 10s per step (instead of 4 s as is the usual routine at ClayLab)
4) Fractionation from 2 g of the whole sample by wet sieving and sedimentation (in Na-polyphosphate): >63 µm, 63-2 µm and <2 µm
5) Exchange of the clay fraction into Ca-form
7) For (clay) mineral identification: XRD of oriented specimens (smear slides from milled 63-2 µm and from the clay fraction on single crystal silicon wafers): simple air dried and after different treatments: ethylene glycol, formamide time dependent for halloysite and kaolinite, guanidine for vermiculite, heated at 350 and 550 °C respectively., Reynolds Cup sample two was also heated after K exchange as a check of HIV
8) Collecting of X-ray pattern of randomly oriented specimen of the 63-2 µm and the clay fraction for a "special look" on the 060 region
Steve Hillier said:
“We were very pleased with our second place position in the 6th Reynolds Cup. Like most other contestant we relied on XRD for the quantitative analysis of the bulk sample. We backed this up by XRD analysis of oriented clay size fractions for precise identification of the clay minerals, applying a standard progression of air-dried, glycolated and heated patterns. For some reason the smectite in sample 1 failed to make an appearance in the clay size fraction and we left smectite out of the bulk analysis including only mixed-layer illite-smectite which was obvious in the clay size fraction analysis. As a result we determined far too much illite-smectite, a lesson there for sure. Our bulk analysis method is based on full pattern fitting of measured experimental patterns. Once you have your experimental patterns this is an extremely powerful method of quantitative mineralogical analysis that we have been successfully applying to soils and rocks for some time now. It probably copes more rigidly with background compared to Rietveld approaches where background is modelled separately. So it was particularly satisfying to accurately quantify the amorphous component in sample 3, which was identified by the absence of ‘enough background’. We have also abandoned the use of an internal standard having reached the conclusion that it gets in the way! The only thing we did differently to our routine methods was to count the patterns for longer and also to make XRF analyses of the samples. These were used a check on the likely accuracy of our mineralogical analysis by assuming compositions for each of the minerals identified and then calculating the chemical composition of the sample for comparison with the actual composition. Our bulk XRD methods or analysis are very firmly based around effort in sample preparation, in particular we believe that preparing all our standards and unknowns by spray drying is at the heart of our continued success in the Reynolds Cup.”
Reinhard Kleeberg and Robert Möckel described their procedure:
“We first took 0.85 g material, ground by hand in an agate mortar and measured an overview powder pattern in order to identify any critical minerals, e.g. water soluble species. For following bulk sample quantification, exactly 0.8 g of this material were mixed with 0.2 g corundum as internal standard and milled in a McCrone mill with zirconia grinding elements in water-free ethanol for 8 minutes. Additionally, 2 grams untreated sample material were dispersed in ethanol and sieved on a 20 micron screen. Both fractions < 20 and > 20 micron were also mixed with 20 wt% corundum, in order to get an independent result from these enriched fractions. The > 20 micron fraction was inspected under a microscope. Some particles have been separated and investigated by SEM/EDX. A part of the < 20 micron fraction was dispersed in water and oriented samples have been prepared by sedimentation on glass slides. No cation exchange procedures were applied. The oriented samples were measured in air-dried, glycolated and partially 400°C and 550°C heated stage. For samples 1 and 3 oriented samples were also prepared for the milled > 20 micron fraction, in order to confirm the presence of smectites in sample 1 by EG treatment and halloysite in sample 3 by formamide intercalation.
Mixed-layer mineral identification was performed by SYBILLA simulation on the EG treated oriented sample 1. The presence of two 1 nm “illite” reflections was recognized but the type of the illite could not be determined later on the powder pattern.
The main phase identification and quantification was done on the side-loaded spiked powders, measured on a URD-6 diffractometer (Freiberger Präzisionsmechanik, from 1988), Co long-fine focus tube, 40 kV 30 mA, energy disperse detector Meteor0D, automatic divergence slit irradiating 15 mm length, 3-80 °2θ, step 0.02, 10 sec/step.
The first phase identification was tried by conventional SEARCH-MATCH software ANALYZE and relational search in PDF-4+, release 2011. The quantification was performed with the Rietveld method using the programs BGMNwin and AUTOQUAN. Minor phases were identified by PC-PDF from the remaining maxima in the Rietveld difference plot.
We tried to apply our most recent structure (and disorder) models as orgeloped by Kristian Ufer for I/S, kaolinite, halloysite, talc and chlorite in the refinements. The sample 3 results of the bulk sample and the weighted fractions agreed well. For sample 2 we noticed big correlation problems of the trioctahedral mineral components, probably by the missing or wrong disorder models and any over-parametrization of our PO correction. This problem could not be solved within the contest, so we had to report any compromise results only. For sample 1 we noticed disagreement of the refinement results for the 2:1 minerals and a big scattering of the calculated “amorphous” content when different models for background were applied and the low-angle region was partially excluded from the calculation. We searched for any direct hint for an amorphous content, but we did not find anything in SEM or by organic carbon analysis. We also tried to “adjust” the chemically characteristic minerals like halite, pyrite + barite, and the carbonates by additional chemical analysis (ion chromatography of a water leachate, ICP/MS on the acid digestion, inorganic carbon analysis), but the balance from chemistry and Rietveld analysis was not precise enough to give an indirect hint to amorphous components. However, as our structure model for the hk bands of the I/S mineral “absorbed” the intensity of the missed illite1Md we consequently overestimated the mixed layer. The reason for the underestimation of the smectites and the misidentification of an amorphous component could not yet be identified. Hoping to get any additional useful information we did run thermal analysis (TG/DTA) in air and nitrogen atmosphere, but this did not help in the confirmation/elimination of the presence of an amorphous component or in the phase quantification.
In the end we learned on the shortcomings of our models for 2:1 minerals. Quantification of I/S seems to be impossible from powder patterns without controlled intercalation in the smectitic layers. The non-basal reflection profile is not specific enough for discrimination from illite. Moreover, the correlation problem of the PO correction models and incompleteness of the trioctahedral mineral structures were identified as critical issues to be resolved in further methodical work.”
2012 Principal Organizers
Mark Raven and Peter Self
CSIRO Land and Water, Adelaide, South Australia, August 2012.
The Reynolds Cup competition is a popular event on the CMS calendar.
The Reynolds Cup has orgeloped into a story of success (sometimes even mentioned as “world championship” in quantitative mineralogy). The participation has increased year on year. Whereas in 2002 from 40 registrants 15 submitted their results (rate 38%) the number increased in 2014 again to 81 registrants from 21 countries with 67 sent in results (rate 83%).
The specific aim of the 7th contest was to evaluate proficiency of analysts working on clay-rich materials representing a sulphate rock (gypsiferous Keuper), an activated bentonite and kaolin clay. The analytical challenges were again numerous. The high amount of phases in each sample (about 20), many of them as trace phases, the presence of different smectite, well and poorly ordered kaolinite beside halloysite as well as of amorphous materials has placed high demands particularly on the qualitative analysis. Furthermore, the sample preparation was a special exercise with the occurrence of different sulphates. Participants were allowed approximately ten weeks to submit their results. As in the last Reynolds Cup, clay minerals/phyllosilicates were judged more strictly by requiring participants to quantify to a greater level of detail in terms of clay mineral/phyllosilicate classification. The entries ranged from 60 to 400% were ranked according to the sum of absolute errors for the three samples which ranges from 60 to 400%. Due to the fact that several entries are within established uncertainties in the compositions of the pure mineral mixtures, the total clay bias, the sum of relative errors, and a penalty for non- and misidentified phases were applied as additional judging criteria to select the one winner.
Click for larger image
The three top contestants were announced at the 51st Annual CMS meeting in College Station, TX in May 2014 and presented with plaques. Only one of them has not been placed at least once in the TOP-3 previously. Interestingly, the 21 TOP-3-places in the RC-history are shared between 11 participants/groups only, which mean some participants consistently achieve excellent results.
Reynolds Cup presentation – from left, Jan Dietel (3rd), Helen Pendlowski and Steve Hillier (2nd), and Michael Plötze (contest organizer)
First Place goes to Reinhard Kleeberg and his coworkers Ulf Kempe and Robert Möckel (TU Bergakademie and Helmholtz Institute Freiberg, Germany). Reinhard is not only placing in the TOP-3 in all but the 2004 contest in which he prepared the samples. He is thus also the first who could repeat his victory in the Reynolds Cup.
The winning team of the 7th Reynolds Cup - from left, Dr. Ulf Kempe, Dr. Robert Möckel, Dr. Reinhard Kleeberg, Sabine Karbautzki, Christine Anders, Kristin Unger (TU Bergakademie and Helmholtz Institute Freiberg, Germany).
Relegated to Second Place only because of the larger clay bias was the team of Steve Hillier with his teammates Helen Pendlowski, Nia Gray, and Ian Phillips. Steve and his team from The James Hutton Institute, Aberdeen Scotland have placed in the TOP-3 in all but the 2010 contest in which they prepared the samples.
The 2nd Place team of the 7th Reynolds Cup - from left, Steve Hillier, Helen Pendlowski, Nia Gray, and Ian Phillips (The James Hutton Institute, Aberdeen, Scotland).
Two entries tied for third place: The group from the BGR in Hannover (Germany) which ended up in the two previous Reynolds Cups on the 5th place could make it on the third place this time. This team including Kristian Ufer (who was formerly working together with Reinhard Kleeberg), Stephan Kaufhold and Reiner Dohrmann had a big advantage with their very recent publication about the mineralogical analysis of activated bentonites and therefore not surprisingly the lowest clay bias on the bentonite sample.
The 3rd Place team of the 7th Reynolds Cup - from left, Kristian Ufer, Stephan Kaufhold, and Reiner Dohrmann (Technical Mineralogy and Clay Mineralogy, Federal Institute for Geosciences and Natural Resources and State Authority of Mining, Energy and Geology, Hannover, Germany).
The other third-placed contestants are Jan Dietel and Jasmaria Wojatschke. They both have never been placed in the TOP-3 previously and are still working on their PhD at the economic geology and mineralogy research group at the University Greifswald (Germany).
The 3rd Place team of the 7th Reynolds Cup - from left, Jasmaria Wojatschke and Jan Dietel (University Greifswald, Institute for Geography and Geology, Germany).
Falling just short of the TOP-3 finishers and thus deserving honorable mentions for their great efforts are Katja Emmerich and Annett Steudel (KIT Karlsruhe, Germany) and again as in the previous 6th RC Rieko Adriaens and Gilles Mertens from Belgium (KULeuven University Clay lab and Qmineral Consulting, Heverlee).
Congratulations to all our participants and particularly to our winners!
XRD was applied as primary tool for identifying and quantifying minerals by more than 90% of the participants. For evaluation and quantification more than half of the participants used the Rietveld-method. As key complementary techniques grain size separation and their separate analysis particularly of oriented samples was applied by almost 70% of the participants. Other additional methods were i.e. chemical analysis and electron microscopy as well as IR spectroscopy and thermal analysis. Only 6% of the participants did not use XRD at all.
Reinhard’s team described their procedure:
Our qualitative mineralogical analysis is based on information from conventional laboratory XRPD and a combination of optical microscopy and SEM/EDX. Especially, the investigation of optically selected particles of the >20 µm fraction by SEM/EDX helped to select or improve the crystal structure models used in the Rietveld quantification. Some minor phases what have been overlooked in the XRPD patterns could be identified in the >20 µm fractions. Moreover, some grains of questionable phases separated under the optical microscope which could not be verified by SEM/EDX were investigated by XRPD and IR spectroscopy to confirm special hypothesis, e.g. halloysite and ferrihydrite in sample 3.
One key method for the identification of the minor phases in the very complex sample 1 was the removal of sulphates and carbonates by EDTA treatment and the analysis of the residual. The identification of clay minerals was done conventionally using oriented samples on glass slides. Several treatments of clays (air drying, Mg and K exchange, ethylene glycol saturation, formamide intercalation, heating) have been applied for identification purposes, specifically to the problems of the individual samples. The identification of the R1 I/S mineral in sample 3 was supported by a manual modelling of the basal series in the EG saturated stage using the SYBILLA software.
The quantitative mineralogy was solely derived from Rietveld analysis (BGMN/AUTOQUAN software), performed on diffraction patterns of McCrone milled, side-loaded powders. These patterns were measured with Co Kα radiation, automatic divergence slit, on a diffractometer system URD-6 built in 1989 but equipped with a Peltier cooled solid state point detector Meteor0D. We measured patterns of the bulk material and of the sieved fractions <20 and >20 µm, each added by 20% of corundum as internal standard for estimating the amorphous content. Approaching consistence between the quantitative results obtained from the bulk sample and from the weighted sum of the fraction was used as criterion for plausibility. We believe that this strategy helps to avoid critical errors of the Rietveld analysis.
As there was not enough material for chemical analysis left and as the benefit of chemical data is limited when complex mineralogical compositions have to be quantified, we did not run quantitative XRF or any other quantitative chemical method. Due to this fact we were not able to set chemical restraints, e.g. for TiO2, PO4 and Sr bearing minerals. Some hints could be derived from semi quantitative SEM/EDX of the powders only.
We are grateful to Michael for putting together such complex samples. Errors like the incomplete identification of clay minerals as well as serious bias in the quantification of the amorphous content are taken for wake-up calls to check our methods critically. Other open questions like a serious differentiation and quantification of 2:1 minerals in complex mixtures also deserve efforts in our methodical work.
Steve Hillier said:
How did we do it? Pretty much the same as in 2012, firstly we sampled about 2.5 grams from the approx. 4.8 supplied and McCrone milled then spray dried these portions at 60°C from ethanol. The powder patterns from these were recorded on a new instrument in our lab that we are keen to calibrate for quantitative work, it's quite a bit of work to run all the standards required, but once it's done for the common minerals, you can slowly add to them over time, as and when you need to. We then set about the identification of the minerals in the powder patterns - spray drying and the resulting randomness of the power patterns allowing us to rely on relative intensities as much d-spacing in the identification steps. At the same time we separated <2 µm clay size fractions from another small portion (about 0.4 g) of the remaining sample, to make a more detailed clay mineral identification, in order to inform the choice of standards to be used for clay minerals in the bulk sample analysis. We also saved the coarser fractions from these clay mineral separates and examined them under a binocular microscope to cross check with the list of minerals identified by XRD. Once we were happy with the mineral identification, we started the quantification process consisting of fitting measured diffraction patterns for all and every mineral identified to the XRD pattern of unknown mixture using the Solver add-in in an Excel program. We iterated through this process trying to improve the fit between measured and calculated (weighted sum) patterns, a process that feeds back to the identification as it becomes quickly obvious if any major minerals have been missed. Finally we made two cross checks, 1) that a chemical composition calculated from our mineralogical analysis would generate a chemical analysis similar to that which we had measured on another small portion (0.9 g) of the sample by XRF, and 2) that CEC values calculated from the mineralogy were similar to those measured on another portion (1.0 g) of the sample by a cobalt hexamine method. Sample RC7-2 had our highest bias, probably due to the calibration of the amorphous phase used in this sample which can easily 'trade' against the di-octahedral smectite pattern, so we underestimated amorphous and overestimated smectite, although we also failed to recognize the minor amount of illite-smectite in this smectite dominated sample.
Reiner Dohrmann summarized the exhaustive procedure with application of many complementary methods as follows:
XRD of untreated material as shipped; inspection with optical microscope; 20 µm or 6.3 µm wet sieving (partly with ethanol); SEM; XRD of bulk material (pure and with 10% ZnO as internal standard); XRD of <20 µm and >20 µm fractions (partly <6.3 µm); XRD (AD and EG intercalated) of oriented specimen, partly at controlled relative humidity (0% - 90%); DTA-MS of bulk materials; Rietveld refinement of bulk and all fractions; LECO C+S determination; IR of bulk and all fractions; CEC determination by Cu-trien intercalation; XRD of bulk and some fractions; calculating normative chemical composition from Rietveld refinement and adjusting with XRF data; specific surface area (only sample #RC7-3); chemical analysis of solutions collected from washed samples during fractionation (anions and cations).
Here is the procedure by Jan and Jasmaria :
First of all we examined the samples by optical microscopy and thereafter using random powder XRD for identifying critical minerals with a tight stability range or well soluble mineral phases. Secondly we took 0.900 g of each sample mixing it with 0.100 g zincite (ZnO) as an internal standard and grinding it with a McCrone micronizing mill with ethanol (agate grinding elements, 8 minutes grinding time).
About 2 g of each sample was used to separate particles <2 µm and >2 µm. Both subsamples were prepared as random powders as well as preferred oriented samples using sedimentation on glass slides. These oriented samples were measured by XRD in an air dried condition and then treated with ethylene glycol at 60 °C fo r 20 hours and thereafter heated to 550 °C. Sample 3 additionally was treated with formamide to distinguish kaolinite/halloysite.
About 2 g of sample 1 was dissolved in distilled water for removal of soluble mineral phases and some HCl solution was added to remove remnant carbonate phases. The remaining sample was again prepared as random powder and preferred oriented sample.
Random powders were prepared by front-loading into aluminum cuvettes and measured on a Bruker D8 Advance diffractometer with Fe-filtered Co radiation, generated at 40 kV and 30 mA, equipped with fixed divergence (0.499°), antiscatter slit (8 mm) and a LynxEye 1D detector.
All random powder samples were first analyzed by using EVA (from Bruker-AXS) with PDF-2 database, release 2009. The following detailed qualitative and quantitative analyses were done with the help of the Rietveld method using the program BGMNwin. Structure models were selected carefully using real structure parameters and model modifications were done to better describe the observed diffraction pattern.
2014 Principal Organizer
ETH Zurich, Switzerland, August 2014.
The 2016 Reynolds Cup was supported by The Clay Minerals Society, the Deutsche Ton- und Tonmineralgruppe e.V. (DTTG), and the Technical University Bergakademie Freiberg.
Once more the Reynolds Cup has seen a big response in the community of mineralogists. Whereas in 2002 from 40 registrants 15 submitted their results (rate 38%) the number increased again to 83 registrants from 25 countries with 69 sent in results (rate 83.1%).
As usual the three samples of the 8th RC2016 were comprised of mixtures of purified, natural and synthetic minerals commonly found in clay bearing rocks and soils that represent realistic mineral assemblages. The specific aim was to evaluate proficiency of analysts working on clay-rich materials representing a shale, a clay-rich tailing, and a weathered/altered ultrabasic rock. This information was relayed to the contestants with their samples. The non-clay minerals and clay minerals/phyllosilicates were judged in groups as in previous RC’s.
The three top contestants were announced at the 53rd Annual CMS meeting in Atlanta, Georgia, in June 2016 and presented with plaques. Here they are:
The team of QMINERAL & KU Leuven / ONDRAF-NIRAS, Heverlee, Belgium
Presenting the Cup: Rieko Adriaens (left) and Gilles Mertens (right)
First place, bias 50.7 %
Rieko and Gilles have formed a creative team and worked permanently on the improvement of their techniques. In previous contest they repeatedly reached ranks close to the top 3, and this year they occupied the throne. Congratulations!
Peter Self and Mark Raven, CSIRO Adelaide, Australia
Second Place, bias 54.2 %
Mark and Peter are working in the field of applied mineralogy and are very experienced in phase analysis of various materials, not only clays. The team already reached the third place in 2008 and won 5th contest in 2010. As active members of the CMS they also contributed to the improvement of methods in our community by supplying nice special clay minerals from Australia to the Source Clay Repository.
Stephen Hillier, Ian Phillips, Helen Pendlowski, Nia Gray
The Hutton Institute, Aberdeen, Scotland
Third Place, bias 57.1%
Since 2002 no Reynolds Cup contest without this team in the top 3 ranks – Steve’s group has demonstrated that superior quality mineral analysis can be provided persistently. This year only the rigid application of the rules for discriminating illite from illite-smectite interstratification, a orgiation of a few percent swelling layers, accounted a significant bias to the evaluation of the results. Without this diminutive uncertainty the team would have won once more with significant margin. Especially impressive are the great results presented by the group for the most complex and complicated sample 8/3.
Traditionally, the RC organizer asks the participants who came close to the top 3 ranks if they agree to be identified to the public, to acknowledge their superior quality work, too. This year we have a shared 4th place:
Carolin Podlech, Markus Peltz, Georg Grathoff, University of Greifswald, Germany
Shared Forth Place, bias 80.0%
This newly formed team, consistig of two students and one experienced researcher, participated for the first time in the RC Contest. Well Done!
Kristian Ufer, Reiner Dohrmann. Jan Dietel and Stephan Kaufhold (absent),BGR Hanover, Germany
Shared Forth Place, bias 81.4%
The BGR team participated in the RC continuously since 2002, was placed second in the first contest, third in 2014, and in all other contests always ranked very close to the top three. The group works actively in orgelopment of methods, and other teams who used the BGMN software will have profited by their efforts. Thanks!
Rieko and Gilles, the QMinerals and KU Leuven team:
As in most laboratories, our mineral quantification procedure relies on 'calculating' an X-ray diffraction pattern and matching it to the measured X-ray diffraction pattern. When reviewing our submissions of previous RC editions, we noticed that, even when using the right compositions and abundances, we could not perfectly reconstruct our experimental X-ray diffraction patterns. The precision of our X-ray diffractogram was therefore not representative enough for the provided mineral mixture. Hence, we decided not only to use the traditional McCrone milling to improve the quality of the diffraction data but also to apply spray-drying. The initial sample was split in four representative parts. Two parts were subjected to size separation in three different size fractions and measured “as such” without any further treatment as we felt this is crucial for correct identification. The large advantage of this procedure is that when treated carefully, the material can be re-used. These two splits (ca. 2g) were then used to prepare powder diffraction patterns used for quantification. The sample was McCrone milled twice and spray-dried. Al2O3 was measured following the external standard method. One split was used for chemical major element analysis. All samples were measured using a traditional Phillips PW1050/37 goniometer connected to a PW1830 generator equipped with Cu-Ka radiation and proportional detector type PW3011/11. For quantification, we traditionally use both Rietveld refinement (TOPAS) and full pattern fitting software (QUANTA) depending on the sample composition. Recently we started using a PONKCS-assisted Rietveld procedure in TOPAS (Bruker) whereby all crystalline minerals are refined as usual. Clays however are modeled as “fixed”, non-refineable structures.
Mark and Peter, the CSIRO team:
Preliminary back pressed XRD patterns of each of the supplied powder samples were run ‘as received’ on our XRD. Sub-samples of ~ 1.5g of each sample were then micronized under ethanol with a McCrone micronizing mill then oven dried at 60°C. After drying, the micronized samples were thoroughly mixed in an agate mortar and pestle to ensure homogeneity. The fine powders were lightly back pressed to minimise preferred orientation and XRD patterns collected on a PANalytical X’Pert Pro MPD using iron filtered cobalt K alpha radiation. Patterns were collected from 3 to 80° 2 theta at 0.017° steps. Total data collection time was ~30 minutes. The process of micronizing the samples under ethanol followed by oven drying partially dehydrates the swelling clay minerals resulting in broad asymmetric 00l peaks. The micronized samples were therefore calcium saturated to restore the 001 peaks of the swelling clay minerals to ~15Å. This was achieved by washing the micronized samples twice with 1M CaCl2, washing with deionised water followed by ethanol (centrifuged at 6000rpm after each step) before oven drying at 60°C. The Ca saturated samples were again thoroughly mixed in an agate mortar and pestle to ensure homogeneity and lightly back pressed into sample holders for XRD measurement. XRD patterns were then re-collected. Comparison of the XRD patterns before and after Ca saturation confirmed there were no water soluble phases present in any of the samples. A further 2g sub-samples of the as received materials were dispersed with 1M NaCl and centrifuged at various speeds to separate <0.2µm, 0.2-2µm and >2µm fractions. The fractions were again Ca saturated and pressed powder and oriented, magnesium saturated and glycerolated specimens were prepared to help identify the clay mineral species. During the centrifugation process, thin, dark particles were found floating on the surface and collected for XRD and SEM with EDX analysis. These particles were found to be amorphous, composed only of carbon and later shown to be anthracite. Quantification was performed using SIROQUANT version 4 with ‘calibrated’ HKL files prepared from several in-house clay standard materials. This was a critical part of the analysis due to the presence of the Mg-rich clay minerals; saponite, talc, antigorite, vermiculite and Mg-rich chlorite identified in sample RC8-3. Elemental analysis of a sub-sample of the Ca saturated materials were determined by Li borate fusion and XRF analysis. This was used to confirm the upper level of Ti oxide phases present and also assisted with the identification of fluorite, apatite and cassiterite in sample RC8-1.
Steve Hillier and the Hutton Institute team:
How did we do it? Basically, like last time in 2014 and pretty much the same as before that in 2012. Our quantification method is based around full pattern fitting of experimental patterns. So the key is having appropriate patterns for all the minerals that are identified. We typically begin by running unprepared ‘as received’ samples on the XRD, but although this may give some indication of the minerals present, we really only make these runs in the excitement of receiving the samples! They are not really useful for anything. Undoubtedly, the best diffraction patterns for phase ID and the subsequent quantification are those prepared next by McCrone milling followed by spray drying of a carefully split portion of the bulk as received samples. Because the spray drying eliminates preferred orientation it becomes possible to rely much more on intensity information as well as d-spacings during mineral identification. Having identified what minerals we can the next step is to start fitting patterns and this process itself also assists with further mineral identification as well as confirming if the standard patterns we are attempting to fit are appropriate for the actual minerals present in the sample. For some minerals in the RC8 samples were needed to make new standards, for example we didn’t have a topaz standard, or a mica that matched the trioctahedral mica in sample RC8-1, so we obtained some new specimens and made up some new standards. One of the big advantages of an experimental pattern fitting approach is that provided your standards are good matches to the unknowns (and the fitting itself is what tells you that) and you are confident of the calibrations for your minerals, there is absolutely no reason to dilute your sample with an internal standard; it just gets in the way! Because background points are also included in the fitting, it also means that experimental full pattern approaches can quantify amorphous phases directly. This can be a big advantage over other X-ray diffraction methods especially when disordered minerals like clays accompany amorphous phases. While fitting patterns we also looked closely at oriented clay fractions separated from small sub samples to identify the clay minerals present. This helps ensure that the random powder patterns chosen for the quantification of the whole bulk sample are as appropriate as possible. Finally, we also made a chemical analysis by XRF and this is used as a cross check on the final mineralogical analysis. The guiding principle here is that any mineralogical analysis must be compatible with the measured chemical composition of the sample. In fact on this occasion, we correctly questioned the accuracy of an XRF analysis with respect to an erroneous silica content provided for us by an external lab (we don’t have our own XRF). We were suspicious of the XRF result because our calculations based on assumed compositions for the minerals identified and their weight fractions indicated considerably less silica than the XRF lab reported; it will make us think twice about using that lab again. The main point however, is that even based on assumed mineral compositions this kind of cross cheek is probably the best way that there is to verify that your quantitative mineralogical analysis is a reasonable one. The one mistake that cost us a big bias penalty was a misidentification of an illite (with about 5% expandability) as an illite/smectite with about 10-15% expandability (Figure 1). In hindsight this was perhaps due to our over reliance on the full pattern fitting of the bulk samples, we should have examined the clay fraction more closely than we did, and it emphasises that quantification has to be conducted hand in hand with precise identification.
Figure 1. An Illite (red trace) like as was in sample RC8-2 versus an illite/smectite (blue trace) as we modelled as in RC8-2.
Once again like previous Reynolds Cups we can only say that we learned a lot about our methods and importantly how we can work to improve them further.
Thanks to the winners for sharing their knowledge, and thanks to all participants for their efforts in raising the level of mineral phase analysis.
2016 principal organizer
Madsen, I.C. Nicola, Scarlett, N.V.Y., Cranswick, L.M.D., and Lwin, T. (2001) Outcomes of the International Union of Crystallography Commission on Powder Diffraction round robin on quantitative phase analysis: samples 1a to 1h. J. Appl. Cryst., 34, 409-426.
Ottner, F., Gier, S., Kuderna, M. and Schwaighofer, B. (2000): Results of an inter-laboratory comparison of methods in quantitative clay analysis. Applied Clay Science 17, 223-243.
McCarty, D.K. IUCr CPD Newsletter 27, 12-16 (2002).
Kleeberg, R., IUCr CPD Newsletter 30, 22-26 (2005).
Omotoso, O., McCarty, D. K., Kleeberg, R. and Hillier, S. (2006): Some successful approaches to quantitative mineral analysis as revealed by the 3rd Reynolds cup contest. Clays and Clay Minerals, 54 (6), 748-760.