Probe Software Users Forum

General EPMA => EPMA Standard Materials => Topic started by: BenjaminWade on July 08, 2019, 09:38:24 pm

Title: Amelia Albite values
Post by: BenjaminWade on July 08, 2019, 09:38:24 pm
Hi all
Simple question, but I was wondering if anyone would be kind enough to let me know what values they are using in their Standard file for Amelia Albite? I have a couple of pieces, one in an old Taylor mount and one in and old P&H mount. I have been using the one in the Taylor mount for a long time now, and was using the following values:

St  735 Albite - Taylor Mount
ELEM:        O       Na2O     Al2O3    SiO2        K2O     CaO
OXWT:     .003    11.458   19.764   68.139    .229    .378
ELWT:    48.700   8.500    10.460   31.850    .190    .270

These match what is on the SPI website.

The other day I decided to start using the Amelia Albite in my P&H mount and noticed that the reference values given in the P&H handbook are different:

St  900 Albite - P&H mount
ELEM:     SiO2     Al2O3    Na2O      K2O        O
OXWT:   68.673  19.499  11.741    .133    -.046
ELWT:    32.100  10.320   8.710     .110   48.760

Of course both the Taylor and P&H values magically total to 100. In addition the P&H reference doesn't give Ca even though it is present in there. Also note large difference in Si values.

I have been using the Taylor mount and Taylor values for some time now and has seemed to be ok. If I use the Astimex Albite (Strickland Quarry, Ct) to analyse the P&H Amelia albite, I get Si and Al values more in line with the Taylor values (Si - 68.08 and Al 19.90).

Cheers
Title: Re: Amelia Albite values
Post by: Probeman on July 09, 2019, 10:31:03 am
Hi all
Simple question, but I was wondering if anyone would be kind enough to let me know what values they are using in their Standard file for Amelia Albite? I have a couple of pieces, one in an old Taylor mount and one in and old P&H mount. I have been using the one in the Taylor mount for a long time now, and was using the following values:

St  735 Albite - Taylor Mount
ELEM:        O       Na2O     Al2O3    SiO2        K2O     CaO
OXWT:     .003    11.458   19.764   68.139    .229    .378
ELWT:    48.700   8.500    10.460   31.850    .190    .270

These match what is on the SPI website.

The other day I decided to start using the Amelia Albite in my P&H mount and noticed that the reference values given in the P&H handbook are different:

St  900 Albite - P&H mount
ELEM:     SiO2     Al2O3    Na2O      K2O        O
OXWT:   68.673  19.499  11.741    .133    -.046
ELWT:    32.100  10.320   8.710     .110   48.760

Of course both the Taylor and P&H values magically total to 100. In addition the P&H reference doesn't give Ca even though it is present in there. Also note large difference in Si values.

I have been using the Taylor mount and Taylor values for some time now and has seemed to be ok. If I use the Astimex Albite (Strickland Quarry, Ct) to analyse the P&H Amelia albite, I get Si and Al values more in line with the Taylor values (Si - 68.08 and Al 19.90).

Cheers

Hi Ben,
I think both compositions could be roughly "correct".  Why do I say this?  I suspect the situation is similar to the infamous San Carlos olivine which has been shown to exhibit a range of compositions as documented by John Fournelle and others:

https://www.cambridge.org/core/journals/microscopy-and-microanalysis/article/an-investigation-of-san-carlos-olivine-comparing-usnmdistributed-material-with-commercially-available-material/29A60B5E119773D4C144B13259607552

It turns out that if one goes to San Carlos, New Mexico and scrounges around, one can pick up pieces of what might be called "San Carlos olivine".  All with a variety of compositions!

I've heard similar things about Amelia albite. That is, someone goes to the Amelia courthouse in Virginia, picks up some pieces of feldspar, calls it "Amelia albite" and distributes it as such. 

Problem is, it's a natural material and it is not exactly consistent in composition. I'm not going to rant on about how we shouldn't be using naturally sourced standard materials, but suffice to say, I think this is part of the reason we can't get our standards to agree with each other.