Hello, after the analysis of volcanic deposits from South-East Asia by DRIFT Spectroscopy, some peaks occur around 1300-1250 cm-1 (please see the attached image). Do you know to which mineralogical compounds they could be associated? How can we interpreted it from a mineralogical point of view? Also this shifting between the spectra (around 1300-1250 cm-1) seems like a slight variations in the crystalline structures. Do you agree?
Thank you in advance for you answers and contributions.
Hi Stoil
Have you referred to these databases?
https://www.mindat.org/min-50468.html
http://rruff.info
http://www.weizmann.ac.il/kimmel-arch/infrared-spectra-library
Elemental analysis (EDX is simplest if available) will help in narrowing down the search. There are more Raman spectra available for minerals in the rruff database however the search tool is handy and some of the minerals have FTIR as well as Raman spectra.
Hi Killian Barton thank you for your suggestion. I checked this database but there is only X-Ray data and not IR spectroscopic data. This site http://rruff.info propose also a very wide database with Raman, IR and X-Ray database. However, we can not search inside following a criteria of specific wavenumber. Is that means that we should check every possible mineral to see if it could or not induce peaks at 1300cm-1.
Yes we have the elemental analysis of these samples. I suppose that your idea is to perform a PLS regression in order to infer the correlation of the absorbance peaks and the elements?
Assuming that these are the strongest bands in your spectrum then the simple inorganic with bands between 1400-1000cm-1 are carbonates, sulphate and silicates. However the position is dependent on the attached metal and degree of crystallinity, hydration, etc. There are usually other weaker bands, often around 950-600cm-1 which can help with narrowing down and/or confirming the material under examinatio.
I'm not sure how PLS of the IR spectra against the elemental data may be used for identification. Raman measurement of the samples, if available, can be carried out quickly as mineral/inorganic materials tend to yield clear and detailed Raman spectra with little fuss.
The Raman data available in the RRUFF database can be narrowed down using the elemental data and a simple correlation test between the measured spectra and those from the database could go a long way toward identifying the minerals you are handling.
Dear Geoffrey Dent , thank you for your replay. The samples are devoid of carbonates (absence of peaks around 1400 cm-1) but, as you suggest, with high silicate contents. The challenge now is to understand if we could be more precise and identify the specific minerals from the silicate groups. Killian Barton ,also thank you for your time and suggestions in this discussion. I will try to figure out this using the RRUFF database. Thank you.
Have you examined the particles of the volcanic deposits using polarised light microscopy to get an idea about mineral type (or types) are present? I would imagine that the assemblage of minerals in the deposits from a known volcanic source are well-documented (e.g., acidic with lots of silica - granitic, or basic with less silica - basaltic). The presence of coloured (possibly pleochroic) minerals would indicate pyroxenes or amphiboles or if the minerals are colourless then that would suggest silicates such as quartz, feldspar, etc. When using analytical techniques, such as vibrational spectroscopy, don't forget that a quick look down a microscope at your sample can give you lots of valuable information about its composition and if it is a mixture, how many phases, etc.
The whole range spectrum would help me to understand the composition.... if you could show it? Do you have transmission or atr spectrum from the sample - in case of DRIFT the bands in higher frequencies are usually more intense then you observe in other techniques so comparing with for example RRUFF is sometimes hard - there you have only diamond ATR FTIR... was that a surface samples ?
Dear Gary Nichols , thank you for the answer. These volcanic areas aren't documented which makes the interpretation more difficult. However, I agree that sometimes we are too much focused on complexe analytical analysis but the answer could be find with microscope or binocular observations. Thank you once again for your suggestions.
Dear Maja Mroczkowska-Szerszeń , here is the entire range. I don't have Transmission neither ATR spectrum. I can perform an ATR correction on the DRIFT spectra but I'm not sure that it will be helpful. The samples were taken from eroded volcanic deposits at depths ranging from 2-4 meters below the topographic surface.
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