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?)