Dear All
Good to hear from Aral.
When he was analysing his sodic pyroxenes in the late 1970's in Jim Longs lab in Cambridge, I (and before me Norman Charnley) was running the system as post-docs.
Most of his analyses were done on the self built EDS system which Jim developed along with Peter Statham - who then went on to Link Systems and Oxford Instruments.
Every six months or so we would recalibrate the system: that meant pumping the detector down and then recalibrating for each element using known standards. There is a circular argument here as we used a known pure jadeite as the standard for Na - so every time we ran a jadeite we got a "perfect" answer! But, as Aral says the omphacites were always spot on too. The stoichiometries always worked well.
We always knew that some phases would misbehave - - but pyroxene was not of them. Nor surprisingly was albite (but that might be explained by the circular argument).
It seems a long time ago - but we went by the physics then (and we do so even more now given that we now have a much better understanding of peak shape etc) but there were very few robust studies of best analytical conditions. I have no intention of teaching Howard to suck eggs - but there is an interesting experiment to run here. Take a known sample and analyse it under different conditions: accelerating voltage, specimen current, detector processing speed (if your detector lets you choose), or even on a cold stage as opposed to not. I am willing to bet that omphacite will not show Na diffusion or detectable Na loss. Now there is a challenge to someone out there - oh, all the things I always wanted to do before I retired but never did!!
Best wishes
Peter
________________________________________
From: Metamorphic Studies Group <[log in to unmask]> on behalf of [log in to unmask] <[log in to unmask]>
Sent: 24 January 2016 20:45
To: [log in to unmask]
Subject: Re: Na loss in pyroxene
Dear Colleagues,
In the late 1970's I analyzed in Cambridge more than 360 sodic
pyroxenes from 40 odd blueschist samples using the microprobe, and
quite a few from blueschists and eclogites since then. There was no
detectable sodium loss.
Aral
Alinti Bruce Yardley <[log in to unmask]>
> Howard
>
> I seem to recall that Bernard Evans used to have a jadeite standard
> for Na when I was learning microprobery from him in the mid 70s. I'm
> afraid I don't have any remaining records of how well it performed
> however!
>
> Bruce
>
>
> Bruce Yardley
> Emeritus Professor
> School of Earth and Environment
> University of Leeds
> Leeds LS2 9JT
> UK
>
> Tel: +44 (0)7745 132560
>
> -----Original Message-----
> From: Metamorphic Studies Group
> [mailto:[log in to unmask]] On Behalf Of day
> Sent: 24 January 2016 03:08
> To: [log in to unmask]
> Subject: [geo-metamorphism] Na loss in pyroxene
>
> Colleagues
>
> Does anyone know of accessible studies of sodium loss (or not) from
> omphacitic pyroxene during microprobe analysis?
>
> Thanks
>
> Howard
>
> Howard W. Day, Professor Emeritus
> The Dept. Formerly Known as Geology
> University of California Davis
> One Shields Ave.
> Davis CA 95616
--
Prof. Aral I. Okay
Eurasia Institute of Earth Sciences and Department of Geology,
Istanbul Technical University, Maslak 34469 Istanbul Turkey
http://web.itu.edu.tr/~okay/
http://scholar.google.co.uk/citations?user=bG8g-5MAAAAJ&hl=en
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