Plagioclase standards

[JohnF]

We have quite a bit of interest here in accuracy of our plag standards, as our crystallographers need EPMA to “truth” their XRD/TEM work! And we are trying to sort thru some issues related to the standards.

They are putting a lot of emphasis on the composition of the Lake plagioclase, and I’ve gone thru the literature and found several different compositions.

1. Peck (USGS) for Emmons (UW here) back in 1940s? wet chem
2. Fahey (USGS) 1966 wet chem
3. Wenk et akl 1980 (repeated in Wenk 1984).
4. Jarosewich (Smithsonian) used an average of 1 and 2
5. UC Berkeley std 305:  uses a mixture of values from all the above

OK all that is a given.

Today in re-re-searchihng my standards, I located a vial wtih 2 crystals of Lake plag from the UCB collection which Donovan genrously suppled me with many years ago. John, was there a large vial which you took those grains from? It has the std number of #305.

Today I also located a vial here with tiny crystals labelled UC 167303.
I am certain the last digit is a 3.
I would like to track down what they are: could they be also Lake plagioclase?
(Did you come up with the standard numbers at UCB?)

[Probeman]

Today in re-re-searchihng my standards, I located a vial wtih 2 crystals of Lake plag from the UCB collection which Donovan genrously suppled me with many years ago. John, was there a large vial which you took those grains from? It has the std number of #305.

Today I also located a vial here with tiny crystals labelled UC 167303.
I am certain the last digit is a 3.
I would like to track down what they are: could they be also Lake plagioclase?
(Did you come up with the standard numbers at UCB?)

Hi John,
I think I had a vial of small crystals that I got from Rudi Wenk of Lake Co, Plagioclase.  Was I at Berkeley when I gave you those?  Can't seem to locate that bottle here in Oregon.  As you say, I aggregated a number of values from the literature for its composition.  The #305 is the standard number I used in my standard database (since it's limited to standards number less than 32K).  Not sure what its UC number is...

The UC 167303 number is a UC Berkeley geology department museum number.  Not sure who you could contact down there now.  The mineral collection is in deep storage the last time I heard and they no longer have a museum scientist that I know of.  I guess you should contact Tim Teague if he hasn't retired yet.

I'm still trying to get a student down there to record his (Tim's) amazing sample prep methods (art) for posterity.
john