I have come through a few literature,were the presence of particular clay mineral has been validated through the Si:Al ratio obtained from EDAX analysis. But, I would like to understand the basic principle behind these classification based on Si:Al ratio. Is there any article that explicitly talks about such classification?
Mathias H. Köster
Thank you for sharing the details sir. Yes sir, I do accept with your view with regards to the use of EDAX analysis for clay mineral identification.
I agree to the right explanation given by Dr. Mathias to the query. Good day!
Well the EDAX results are only surface mapping results and most of the time obtained results of EDAX vary in the same sample at different locations. My most of work is on vermiculite clay minerals and as for as I know that there are many types of vermiculite only, depending on its origin and structural compositions and amount of impurities or mica present in them. But making a Si:Al ratio sheet which could identify the clay mineral types is not difficult (not 100% accurate but you will have a range of ratio), then only problem would be accuracy of EDAX results.
It is a crude method, but it works. Try and use an EXCEL spreadsheet, take your atomic weight contents form SEM/EDX of O, Si, Na, K, Al, Mg, and Fe (can be supplemented). Calculate some element ratios such as O/Si, Si/Al, Si(Fe+Mg+(Ca)), Na/Al, K/Al and normalize them to an ideal kaolinite, biotite, muscovite etc. by means of the “data sorting” command and you will obtain some kind of a “best fit”. It will not be suitable if you want to publish your data in “Clay minerals” or anything like that but to get an idea of the predominating clay mineral in a sandstone or any other sediments it works. Complex chlorite and smectite s.s.s. are hard to distinguish as it is the case with mixed-layers. But it is better than nothing. It is a geologist´s method if you have no access to XRD, spectroscopy ..
Separation of the light grain clay minerals from the heavy grain counterparts, and the SEM/WDX (EPMA) analysis of some selected light grain clay minerals follow by atomic weight calculation of the Si/Al ratio may be more accurate than the EDAX analysis. Although it is very cumbersome. XRD and TEM analysis remain the best approach.
Sriram Karthick Raja .P Si:Al ratio or even geochemical analysis using EDAX solely can't be used to identify clay minerals. Some clay minerals show quite similar chemical composition, which can only be differentiated using XRD method. This problem will arise if the clay mineral is not of pure quality. Even minor interstratification can alter your result. Thus, it is always recommend to use XRD for identification of clay minerals and then add the EDAX analysis as supporting evidences.
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