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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