Hello all,
I am a current MS student completing the thesis project on the transformation of smectite to illite within mixed layer Illite/Smectites with depth and its relation to thermal maturity. I have a good handle on the preparation of the clay fraction, but have several questions on the correct treatments necessary to get at the data I am needing. I am currently planning on extracting the clay minerals via centrifuge and transferring to glass slides by the vacuum and filter method. So far, I know that I must run both air-dried and glycolated samples, but am unsure if heat-treated samples are necessary for the clay minerals involved. The clay minerals I expect to encounter are illite, kaolinite, chlorite, mixed layer illite/smectite, and possibly a very small amount of Illite/Chlorite/Vermeculite. I am under the understanding that mixed layer Illite/Smectite is easily identifiable from their EG diffraction pattern and does not share peaks with the other clay minerals involved. Therefore, My main questions are as follows:
1. Are heat-treated samples necessary to distinguish between the clay minerals that are expected to be present, or can all needed identifications be completed by comparing the air-dried and EG diffractograms?
2. If heat treatment is necessary, is only 1 heating to 375 degrees C sufficient? From my research, it seems that identification of all expected mixed layer clays collapse at this temperature, and the remaining two minerals, chlorite and kaolinite, can be identified by the chlorite (004) and kaolinite (001) peaks in the air-dried state.
3. If I am advised that heating to 550 degrees C is necessary, is it acceptable to skip heating to 375 degrees separately and simply do one heating stage at 550 since none of the clays included react differently between the 375 and 550 heatings?
Any help is greatly greatly appreciated. I am attempting to complete this project without the guidance of a clay mineralogist, as there are none employed at my university. As I stated above, I believe I am competent in understanding the data I will receive from the XRD analysis, I just simply cannot find a solid answer on what treatment steps are necessary. Time is certainly an important factor for my project deadline, so I would hate wasting time on unnecessary treatments and the re-running of samples. Thank you for taking time to read my question.
Zachary Strong
The University of Akron
Mr. Strong,
your explanation to the main header shows that your clay mineralogical problem is not a simple one and that you obviously study clay mineral content as a function of depth with smectite-illite ratios as a crucial couple to identify diagenetic changes and P-T variation. Therefore I suggest a more advanced study with the XRD analyses added up with IR, temperature-XRD and SEM/EDX+WDX. To get a continuous lithology showing the changes of the smectite/illite ratio I suggest using the CEC for the fine-grained particle size fraction. You can plot it along with K, U and Th. I recommend this because all three elements can be measured by gamma-spectrometry and so you can analyze a larger set of samples than with the routine methods. You have to split your samples into two batches, a "vertical" batch for the creation of a clay mineral log based on rapid-reaction methods and a "horizontal" batch of samples which is investigated in more detail using all methods at hands from routine XRD to EMPA. This strategy is based upon my experience I gathered during the German Continental Deep Drilling Program.
Should you need more help or my answer is considered too evasive let me know that.
Glückauf !
H.G.Dill
Mr. Dill,
Thank you for your quick response. I failed to mention that I have already preformed ESEM imaging/EDX analysis, bulk powder XRD, and also taken measurements of the total organic and inorganic carbon present in each sample to help support the clay fraction XRD analysis. Due to limitations on available equipment and time to complete the project, I do not think I would be able to incorporate IR analyses. My main plan for evaluating I/S ratios is from the peak positions of the I/S mixed layer clay in the glycolated state as advised in Moore and Reynolds (1997). My primary confusion right now is the dehydration steps necessary to correctly identify the remaining clay minerals. I should be able to differentiate between illite, smectite, illite/smectite and illite/chlorite between the air dried, EG, and samples heated to 375 C, leaving only the proportions of discrete chlorite and kaolinite unknown. Hosterman and Whitlow (1983) claim that these two minerals can be identified in the air dried state by their double peak at 25° 2theta. Due to this, I am unsure if another heat treatment to 550 C is necessary, and this is what I am trying to find an answer for. I apologize if my question seems rather dull witted, but I would greatly appreciate if you can offer any guidance on that matter.
Thank you again,
Zac Strong
Zack
Treatment is necessary to separate the two 7Å minerals, kaolinite and chlorite (OK, 14 Å, but there is a 7Å "chlorite", berthierine). We used to employ acidification as this will dissolve the "chlorite" (in sedimentary systems an Fe mineral). If a 7Å peak remains, it is kaolinite.
I'd reinforce Dr Dill's comment that you should try to get additional chemical compositional data. Combining XRD with any additional chemical data, whether individual mineral compositions (EMPA) or bulk chemistry of the powder (XRF, ICP-MS), will allow you to quantify the amounts and compositions of XRD identified minerals more accurately. In essence, the mineral modes multiplied by their chemical compositions MUST equal the bulk chemical composition (matter is conserved). Although data are rarely (never?) exact enough for an exact solution, linear programming (for example, LPNORM, attached is one method) will give constraints on possible solutions.
Regards,
Ian
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