5th RC Competition

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.

So how did they do it?

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.