Calcite dolomite misindexing in EBSD-EDS coupled analyses

[Matteo Demurtas]

Hi everyone,

I'm having problems in processing coupled EBSD and EDS measurements on experimental mixed calcite-dolomite gouges. The quality of the EBSD data is good, despite a hit rate ranging between 50-65%, mostly due to porosity and very fine grained material of the samples ( grain size <1 um). The dolomite grains are incorrectly characterised by a more or less thick rim of calcite (and spurious pixels inside). This error is mostly due to the activation volume of the EDS, which on the borders collects data both from the dolomite grain and the surrounding matrix (calcite rich) resulting in an incorrect phase recognition in these areas.

This is a problem for the interpretation of the orientation of the calcite within the maps, since data include the "fake"-calcite too.

I'd like to know if someone knows some ways either to get rid of these misindexed points or change them into dolomite (still maintaining the orientation though).

Moreover, in the analysis I'd like to maintain the non-indexed areas, limit the grain to the minimum necessary.

I have attached a band contrast image of one small map and the phase map. In the latter you can see how the dolomite grains are surrounded by a rim of calcite (thicker as smaller the dolomite grains are) and some pixels within the grains too.

Any suggestion and help is welcome.

Cheers,

Matteo

[ruediger Kilian]

Hi Matteo,
you could try and calculate grains and remove grains with you one or two pixels(assuming those are the misindexed rims for example). e.g.: ebsd_cleaner=ebsd(grains(grains.grainSize >=3))
To change the phase ebsd(whatever condition).phaseId="phaseID of dolomite"
Hope this helps.

Cheers,
Rüdiger

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> <band_contrast.jpg><ebsd.jpg>

[Matteo Demurtas]

Thank you for the help. I've managed to change only the phase property of pixel wrongly indexed as calcite instead of dolomite (or the other way around in other maps) as a function of the phase of the surrounding pixels. It works fine and with few runs the fake-rims almost disappear. Then the remaining pixels can be deleted with noise reduction.

However I found it's a quite fast method for small maps (for 1e+5 pixels it takes about 20 mins each run), but it's really time-demanding for bigger maps (for 1e+6 pixels around 24 hours per run).

Do you have any suggestion on how I could speed up the process, since it requires to analyse the surrounding 8 pixels for each pixel in the map?

Cheers,

Matteo

------------------------

Matteo Demurtas

Ph.D. student

University of Padova

Department of Geosciences

via G. Gradenigo, 6

35131, Padova (Italy)

Skype: matteodemurtas

Fault rocks!

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[Rüdiger Kilian]

Hi Matteo,
can you give an example how you do it? Are you using a loop somewhere?
Cheers,
Rüdiger

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From: mtex...@googlegroups.com [mtex...@googlegroups.com] on behalf of Matteo Demurtas [matte...@gmail.com]
Sent: Friday, June 24, 2016 1:25 AM
To: mtex...@googlegroups.com
Subject: Re: {MTEX} Calcite dolomite misindexing in EBSD-EDS coupled analyses