I felt concerned to understand the merit and probable usage of relative data showing concentration of elements in a sample (normalized data for oxides in wt%) relative to actual (absolute) concentrations as obtained from microprobe analysis.
Am worried about this because, after due calibrations and repeated analysis, their is precision is very good (several attempts give nearly same results) but am worried if these are true values (if accurate) because nearly all summed total are far less than 100 wt%.
Values like 89.9 wt% for my Fe-Ti oxide minerals, 91, 92, 93 wt% for my amphibole, mica and feldspars respectively
Dear Kayode,
If you have used a proper standard during your analysis and confident that the microprobe is giving you accurate results, the lower totals are very likely the result of Fe+3 presented as Fe+2 in the analysis. One way to get an estimate of the problem is to do a theoretical calculation and compare with your analytical result.
I made such calculation as an example at the following link:
https://www.researchgate.net/post/Microprobe_magnetite_iron_oxide_recalculation_and_acceptable_analytical_totals
Particularly, ilmenite contains 50% FeO and 50% TiO2 by weight and some of your Fe+2 may be actually Fe+3 and may contribute to your problem of low totals. Similarly, feldspar may contain Fe2O3 which will have the same effect.
Hope this will help you.
LRK
