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Techniques for CollectorsRaman Spectroscopy

17th Jul 2013 18:10 UTCReiner Mielke Expert

How many matching peaks does one need to call two things the same? Attached are two spectra both of Tritomite-Ce taken from RUFF but only three peaks match?

17th Jul 2013 18:38 UTCAlex Homenuke Expert

Difference in filtering??

17th Jul 2013 19:13 UTCOwen Lewis

Reiner,

You are looking at analogues of molecular vibration within different samples of the same mineral . The mineral you have selected has a relatively complex chemistry (and structure) The pattern created depends on the on the molecular makeup of the area of the sample under test the orientation of the sample and other factors. The traces here show differences in composition (and or attitude) as well as similarities. You need to decide what makes a 'good; sample for your purposes and then look for the response peak that such a known good sample shows. Can you see all the peaks that should be present in an analogue trace for it If you can't, which peaks are missing and what to the missing peaks represent and what is the significance of the missing information to you. That's before getting to the causes of activity you can see detected, that do not associate with the theoretical perfection of the substance you test for.

Raman analysis is not to be picked up from a book over a wet week-end. It takes experience and the building up of much information . Driving the instrument needs only a good technician. Supervising and interpreting the output requires experience and a post-grad standard of education in the relevant sciences.

17th Jul 2013 20:39 UTCStefan Oertel

Rainer, if you take a close look to R060370 it says "Status: The identification of this mineral is not yet confirmed". Until it is confirmed we might talk about two different minerals. Better wait until you get the measured chemistry of R060370, then compare it with R060046, then draw conclusions.

Cheers,

Stefan

18th Jul 2013 01:34 UTCReiner Mielke Expert

Thank you Stefan,

I guess if it is confirmed then 3 peaks is sufficient and my question is answered. However I would have thought that such experiments had already been done on other minerals and someone could tell me if this is generally the case.

Thank you Owen,

Let me rephrase my question. Assuming that the people at Ruff who produced the spectra are competent and that the results are representative of the minerals tested, are the two patterns sufficiently different to be able to conclude with 90% confidence that the samples analyzed are of two different mineral species?

18th Jul 2013 09:59 UTCUwe Kolitsch Manager

Reiner: partial metamictisation also changes Raman spectra considerably.

Your rephrased question cannot be answered. One would have to know all available data on the samples (e.g., chemical homogeneity, crystalline state, submicroscopic impurities etc.).

18th Jul 2013 14:02 UTCReiner Mielke Expert

Thank You Uwe that was very informative. Unfortunately it would seem that RAMAN is not very useful for metamict minerals.

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