My soil sample is an A-7-5 tropical red earth, classified as SC using USCS classification scheme. In the attached XRD results I couldn't find 7.2Angstrom peak for Kaolinite clay mineral, only 3.34A suggestive of Quartz. I also observed another peak of 4.24A, and could not place where it really belongs.
I could not also tell whether the TGA result supports the presence of Kaolinite and Quartz as reported by other authors for similar tropical red earth soils.
I would be grateful for any clarification or guidance provided by anyone of you dear researchers.
Thank you
HI, I am not sure you can tell from the attached data alone. If so I will be curious to read from someone that can offer that.
However, to attempt to be a bit helpful, I found the included article that seems that their method might be something you could try. It looks like their method might be something you could try that might give you the detection you are seeking. https://www.persee.fr/doc/sgeol_0302-2684_1990_act_89_1_2202
Hi Endurance,
You're right to worry about the identification. The ~7A peak is characteristic for kaolinite, and it's hard to see why it would be missing. Maybe a peculiar texturing? You can try to change the powder orientation in your sample - e.g. pressing a pellet to get the platelets mostly aligned parallel to each other and perpendicular to the beam plane. That would tend to emphasize the (00l) line, and if it's still missing it would be a strong argument against kaolinite.
In addition, you would expect to see a weight loss of about 12-13% (water) between 100C and 600C (transformation to meta-kaolinite, theoretic loss 14%), and you only see about 6.5%, so if kaolinite is present it's ~50% of the sample.
I would consider clays with much larger "c" spacing and lower % water loss on heating.
I'm absolutely grateful @ Emanuel Cooper for your detailed response. Thanks for the suggestions given.
through multiphase fitting u can examined the presence of kaolinite by using rietveld through qualx , match and with fullprof also.
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