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THE MODIFICATION AND APPLICATION OF THE QUANTITATIVE X‐RAY DIFFRACTION METHOD OF SCHULTZ (1964) TO THE MINERALOGICAL STUDY OF LONDON CLAY SAMPLES
Author(s) -
BURNETT A. D.
Publication year - 1974
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1974.tb01114.x
Subject(s) - illite , mineralogy , quartz , clay minerals , mineral , reproducibility , intensity (physics) , geology , sample preparation , sample (material) , analytical chemistry (journal) , materials science , mathematics , chemistry , statistics , metallurgy , optics , environmental chemistry , chromatography , physics , paleontology
Summary Over 300 samples of London Clay from twenty‐one widely scattered sample locations in the London and Hampshire Basins were to be examined in detail by X‐ray diffraction techniques. The quantitative method of Schultz (1964) was chosen as being most suited for the analysis of the samples. Series of tests designed to investigate the reproducibility characteristics of the method were conducted. These showed that the sampling, sample preparation, and interpretation procedures used all introduced cumulative reproducibility errors of roughly equal magnitude which completely overshadowed errors introduced by machine‐response variation. It was also established that minerals whose contents were below 10 percent of whole sample failed to be consistently quantitatively estimated. The accuracy of this method of analysis depended heavily on Schultz's quoted ‘intensity factors’ which were involved in the calculation of individual mineral contents. The authenticity of these factors with regard to the London Clay suite of minerals was checked by comparing accurately determined mineral percentages of six standard London Clay samples with the results obtained by use of the Schultz procedure and factors. The method was found to be basically sound although the intensity factors for quartz, total clay minerals, carbonates, and illite had all to be slightly adjusted. The accurate quartz percentages were established by three different X‐ray diffraction techniques and the carbonate percentage checks were accomplished by specially designed wet chemical methods. The total clay mineral and illite contents checks were carried out by back‐calculation of the Al 2 O 3 , and K 2 O percentages as determined from full wet chemical analysis. Using the adjusted factors, quartz percentages are estimated accurate to ±6 percent, total clay minerals to ±7 percent, carbonate percentages to ±1.5 percent, and illite contents to ±4 percent of the whole rock.