Chernovite analysis doesn't add up

Hi,

I'm hoping someone here might be able to give me some suggestions. I've found some Chernovite (Y) using an SEM but I have some problems with the anlaysis. I have found it in several samples, but it is very small - mostly <50um. Two of the first specimens I found gave me very good analysis of nearly 100% but now I have another polished block with quite a lot of material on and the totals only come to about 85%

Here is one of my sets of results:
7.76 P2O5
0.58 V2O5
30.16 As2O3
32.72 Y2O3
4.96 Gd2O3
5.82 Dy2O3
2.89 Er2O3
84.49 TOTAL

I'm new to using the SEM and this is the first exciting thing I've found so am I doing something wrong ?

I have just read an article about hydrated chernovite so I am wondering if that is what I have here? If so am I damaging the chernovite by analysing it?
Could it be another mineral and I am missing an element or two?
Is one of my calibrations out for one of the elements maybe?

I have tried XRD on the polished blocks but so far it hasn't picked up chernovite. I've looked down a microscope and I can't quite see where it is by eye so I might try XRD again on a different area.

Does anyone have any suggestions ?

This is a new location for chernovite so I'm hoping I can get some good data for it.

Thanks

Helen

If you are damaging it, you should see some pits in the specimen where it was analyzed. At a quick look, it appears that both the cations and anions are low (so you probably are not missing some element). If you aren't getting any damage, I might look to see if there was some charge buildup on the sample.

Finger oils??

You need to get a good ground on a sample else electrons will build up and tend to deflect the electron beam. Most specimens need to have a carbon or gold coating to provide enough electrical conductivity.

You might also be unlucky enough to have just a thin sliver of the mineral on the surface, but this tends to be a lot more unlikely.

Finger oils- carbon contamination from handling the speciemen.

Hi,

Thanks for your replies. It was carbon coated, but it isn't a very good polished resin block. Because the specimens are very small and in a vug I didn't lap the surface of the resin block down very much, I then looked at it and found quite a lot of the chernovite. I've since lapped it again to get a better surface, but I'm now worried I'll loose everything so I'm doing it in stages. It sounds like this could be the problem -in that I haven't got a good surface yet, in fact there may even be some resin still there. I'll try lapping it a bit more and see if it gets better. Nothing's obvious to me under the binocular microscope but it is very small!

Thanks

Helen

The poorly polished surface is probably to blame - a common cause of low totals.



Edited 1 time(s). Last edit at 12/30/2011 01:52PM by Uwe Kolitsch.