R.D. Knight and R. A. Klassen

Mineralogical analyses establish the properties, provenance, and weathering history of soils and sediments, and are basic to geology, agriculture, the environment, forestry, and natural resources. For fine-grained materials, X-ray diffraction (XRD) analyses of clay-sized (<0.002 mm) and silt and clay-sized (<0.063 mm) fractions, and petrographic and microbeam analyses of coarser (0.425-2 mm) fractions are commonly used. However, particulate mineralogy can be difficult to characterize due to (1) fine grain sizes (e.g., <0.063 mm), (2) organic matter, (3) secondary, amorphous salts and Fe and Mn oxides, and (4) weathering of minerals. XRD methods are effectively limited to minerals comprising >5 wt% of the sample (Minnis, 1984), and can be difficult to apply for grains larger than silt-sized (>0.063 mm) unless the sample is crushed.

Petrographic and microbeam approaches focus on individual grains, incorporating varied geochemical and morphological parameters for mineral determinations. Scanning electron microscopy (SEM) using backscattered electron (BSE) and energy-dispersive X-ray (EDS) spectrometry images have often been used to map elements and to determine grain separations, boundaries, and shapes (Hall and Lloyd,1981; White et al., 1984; Pye, 1984; Pye and Krinsley, 1984; Dilks and Graham, 1985; Mainwaring, 1989; Tovey et al., 1989; Petruk 1989a, 1989b; Nadeau and Hurst, 1991; Tovey and Krinsley, 1991, 1992; Protz et al.,1992; Tovey and Hounslow, 1995; Krinsley et al., 1998). At the Geological Survey of Canada a methodology for combining EDS element image maps has been developed to determine quantative soil mineralogy of particulate matter (Knight et al., 2002).

EDS image analyses comprises four steps:

1. image acquisition
2. processing and enhancement
3. image analyses
4. mineralogical interpretation

The original and processed image files are stored in a nested series of folders which reflect the processing sequence and expedite file loading, image enhancement, and mineralogical interpretation. The original EDS image files are used to resolve complex mineral interpretations.

References

Dilks, A. and Graham, S.C. 1985
Quantitative mineralogical characterization of sandstones by back-scatter electron image analysis. Journal of Sedimentary Petrology, v.55, p.347-355.

Hall, M.G., and Lloyd, G. E., 1981
The SEM examination of geological samples with a semiconductor back-scattered electron detector. American Mineralogist, v.66, pp.362-368.

Knight, R.D., Klassen, R.A., and Hunt, P. 2002
Mineralogy of fine-grained sediment by energy-dispersive spectrometry (EDS) image analysis - a methodology. Environmental Geology, v. 42, pp32-40.

Krinsley, D.H., Pye, K., Boggs, S.Jr and Tovey, N.K., 1998
Backscatter scanning electron microscopy and image analysis of sediments and sedimentary rocks. Cambridge University Press, 193 pp.

Mainwaring, P.R. 1989
A review of image analysis applications in petrology, In: Petruck W (ed) Short Course on Image Analysis Applied to Mineral and Earth Sciences: Mineralogical Association of Canada, Ottawa,Ontario, pp 76-85.

Minnis, M.M., 1984
An automatic point-counting method for mineralogical assessment. The American Association of Petroleum Geologists Bulletin, v.68, pp.744-752.

Nadeau, P.H. and Hurst, A. 1991
Application of back-scattered electron microscopy to the quantification of clay mineral microporosity in sandstones. Journal of Sedimentary Petrology, vol.61, pp. 921-925.

Petruk, W. 1989a
Image analysis of minerals, In: Petruck W (ed) Short Course on Image Analysis Applied to Mineral and Earth Sciences: Mineralogical Association of Canada, Ottawa, Ontario, pp 6-18.

Petruk, W. 1989b
The MP-SEM-IP image analysis system, In: Petruck W (ed) Short Course on Image Analysis Applied to Mineral and Earth Sciences: Mineralogical Association of Canada, Ottawa, Ontario, pp 37-43.

Protz, R., Sweeney, S.J., and Fox, C.A. 1992
An application of spectral image analysis to soil micromorphology 1. Methods and analysis. Geoderma, vol. 53, pp.275-287

Pye, K. 1984
Rapid estimation of porosity and mineral abundance in backscattered electron images using a simple SEM image analyzer. Geological Magazine, vol. 121, pp. 81-136.

Pye, K. and Krinsley, D.H. 1984
Petrographic examination of sedimentary rocks in the SEM using backscatter electron detectors. Journal of Sedimentary Petrology, vol. 54, pp.877-888.

Tovey, N.K. and Hounslow, M.W. 1995
Quantitative micro-porosity and orientation analysis in soils and sediments. Journal of the Geological Society , London, vol. 152, pp.119-129

Tovey, N.K. and Krinsley, D.H. 1991
Mineralogical mapping of scanning electron micrographs. Sedimentary Geology, vol. 75, pp.109-123.

Tovey, N.K., Smart, P., Hounslow, M.W., and Leng, X.L. 1989
Practical aspects of automatic orientation analysis of micrographs. Scanning Microscopy, vol. 3(pp. 771-784.

White, S.H., Shaw, H.F., and Huggett, J.M. 1984
The use of back-scattered electron imaging for the petrographic study of sandstones and shales. Journal of Sedimentary Petrology, vol. 54, pp. 487-494.