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X-ray diffraction (XRD)

X-ray diffraction pattern analyses can be done in the laboratories of the research group Crystallography (University of Bremen, Dept. of Geosciences) overseen by Dr. Christoph Vogt.
Dried bulk samples have to be grounded to a fine powder (<20 µm particle size to prevent particle size effects) and will be prepared with the Philips backloading system to prevent any kind of orientation. A thorough preparation commonly increases reproducibility of the results, however, the standard deviation given by Moore & Reynolds Jr. (1989) of ±5% can be considered as a general guideline for mineral groups with >20% clay fraction. In addition the determination of well crystallized minerals like quartz, calcite or aragonite can be done with better standard deviations if calibration curves are available (Tucker 1988).

The X-ray diffraction can be measured on a high end Philips X’Pert Pro multipurpose diffractometer equipped with a Cu-tube (k(alpha) 1.541, 45 kV, 40 mA), a fixed divergence slit of (typically) ¼°, a 16 samples changer, a secondary monochromator and the X’Celerator detector system. A typical measurement of bulk material powder can be done as a continuous scan from 3 – 85° 2theta, with a calculated step size of 0.016° 2theta (and for example calculated time per step of 100 seconds).
This will lead to a measuring time of 1 hour per sample (compared to about 2.5 h with a standard scintillation detector). Therefore, one can calculate with approx. 23 samples per day if the lab is fully dedicated to the onshore science party work.
Of course, other measuring programs can be run as well. In cooperation with other laboratories clay fraction separation and preparation would be an option. Please note that this has to be announced far in advance.

The measurement is only the first step and mineral identification and (semi-) quantification has to follow.
For the mineral identification, the Philips software X’Pert HighScore™ is available, which, besides the mineral identification, gives a semi-quantitative value for each identified mineral on the basis of Relative Intensity Ratio (R.I.P)-values. The R.I.P.-values are calculated as the ratio of the intensity of the most intense reflex of a specific mineral phase to the intensity of the most intense reflex of pure corundum (I/Ic) referring to the “matrix-flushing method” after Chung (1974).
If necessary also the full analysis can be performed (e.g., IODP 302, Backman et al., 2006).
In addition, more sophisticated quantification techniques (full pattern, Rietveld) are available.
For fast identification and visual analysis of measurements we also recommend the AppleMacIntosh freeware MacDiff.

For further information and additional opportunities visit the homepage of the Research Group Crystallography (University of Bremen, Dept. of Geosciences).

Backman, J., Moran, K., McInroy, D., Mayer, L.A. and IODP Expedition 302 Scientists (Editors), 2006. Arctic Coring Expedition (ACEX): paleoceanographic and tectonic evolution of the central Arctic Ocean. IODP Proceedings volume, 302. Published by Integrated Ocean Drilling Program Management International, Inc., for the Integrated Ocean Drilling Program, prepared by European Implementing Organization, ESO Coordinator, British Geological Survey, and U.S. Implementing Organization Science Services, Texas A&M University, Edinburgh, 396 pp.

Birkenstock, J., Fischer, R.X. and Messner, T., 2006. BRASS, the Bremen Rietveld analysis and structure suite. Zeitschrift für Kristallographie, 2006(suppl_23/2006): 237-242.

Chung, F.H., 1974. Quantitative interpretation of X-ray diffraction patterns, I. Matrix-flushing method of quantitative multicomponent analysis. Journal of Applied Crystallography 7: 513 - 519.

Petschick, R., Kuhn, G. and Gingele, F.X., 1996. Clay mineral distribution in surface sediments of the South Atlantic: Sources, transport, and relation to oceanography. Marine Geology, 130(3-4): 203-229.

Vogt, C., Knies, J., Spielhagen, R.F. and Stein, R., 2001. Detailed mineralogical evidence for two nearly identical glacial/deglacial cycles and Atlantic water advection to the Arctic Ocean during the last 90,000 years. Global and Planetary Change, 31(1-4 (QUEEN Special Issue)): 23-44.

Vogt, C., Lauterjung, J. and Fischer, R.X., 2002. Investigation of the clay fraction (<2 µm) of the clay mineral society reference clays. Clays and Clay Minerals, 50(3): 388-400.