[meteorite-list] XRF issues response to Dan Wray

From: Impactika at aol.com <Impactika_at_meteoritecentral.com>
Date: Tue, 15 Mar 2011 17:20:22 EDT
Message-ID: <3f5f5.773c574f.3ab13216_at_aol.com>

On behalf of Blaine Reed who is not (yet!) a member of the MetList.
Anne M. Black
_http://www.impactika.com/_ (http://www.impactika.com/)
_IMPACTIKA at aol.com_ (mailto:IMPACTIKA at aol.com)
President, I.M.C.A. Inc.
_http://www.imca.cc/_ (http://www.imca.cc/)
 
 
In a message dated 3/15/2011 2:00:19 PM Mountain Daylight Time,
brmeteorites at yahoo.com writes:
Dan,

I wanted to reach you to talk with you a bit about this, but I have no
phone number for you, only a mailing address. As I am leaving (tomorrow morning,
supposedly) to deal with the aftermath of yet another death in the family
(the third in the past year now), I don?t have time to take to research
contact info. Also, your comments could be considered rather disparging towards
my efforts in this field by some (Carl definitely though so, and was the one
to drop this bomb in my lap) ? so I need to state my case publicly anyway. I
am having Anne send this out for me for me.

Some of what you say is indeed true (I?ll go into that here in a bit), but
much of your comment leads me to believe that the machine you are running
does not have the proper programming in it.

These things come with a number of analysis ?program? options. I believe
that the ?Alloy?(indeed mostly for analysis work on man-made metals, but I
have had quite good results on iron meteorites using this ? more on that
later) comes from the factory on all of them. The ?extra? programs often cost
substantial extra dollars and many buyers fail to add the ones that are most
useful for the job they really want to do. The company I got my unit from
(Innov-X) allows you one free additional program. Any additional programs (of
which we hope to add a ?meteorite identification? program to the list of
potentials at some point) run $2500 to $3500 each, I believe. The devil is in
the detail of what extra programs are on the machine being used.

I really hate to make public just what is the proper programming at this
point, but I really don?t see that I have much choice while addressing your
comments.

For irons: ?Alloy? is fine! However, it is probably NOT a good idea to let
the machine go over to the second beam (the one that sees the light
elements like Aluminum, Magnesium) as this often (but not always) really screws up
the results. That second beam is really meant to run when you already know
that the material you are looking at is indeed mostly Al and Mg. These light
elements are indeed VERY hard for these machines to nail down accurately (in
ANY programming mode) unless you are indeed looking at a man-made material.
MANY other elements do indeed interfere with the detection of these! This
has made my job A LOT harder as I thought that by getting some kind of
accurate Mg amount might allow me to make an estimate of a faylite number (but I
would have to have also found a way to ?back out? the fresh metallic iron
from the sample analysis results first). Unfortunately, I will not be able to
do this.

I don?t understand how you are not getting anything remotely accurate for
Ni content of irons with your machine (assuming you have an ?Alloy? mode). I
have gotten quite good results from mine. I have consistently (on cut
surfaces, weathered surfaces give somewhat skewed results ? a bit on that in a
later note) gotten results shockingly close to actual published results. In
fact, my results where so accurate (down to even seeing the gallium and
germanium on the graph in proper peak height relation ? those were not turned on
in the particular alloy program I was using) on a Canyon Diablo end piece I
had that it prompted Dr. Carleton Moore to come back to the show a few days
later with a couple other sample to run for him!

I do indeed ?look at the graph? from time to time (mostly when I get a
real screwy number on something). I had Rob Wesel bring me a chunk of slag (it
had crystal structure in it superficially resembling Widmanstatten lines on
the cut face). My initial analysis tried to tell me that it had some 24%
Iridium! (at around $1000/ ounce, that would make it one valuable rock!).
Knowing this to be highly unlikely, I went ?to the graph?. I quickly saw that
what I really had was arsenic. This element is not turned on for detection in
the alloy mode, so the thing saw it as iridium, as those two elements do
share one of their peaks (and the program will automatically assume it is
looking at material that is consistent for the program being run).

This definitely proves your point of needing to look at the graph if
something seems amiss (and it is not a bad idea to have a look at it from time to
time even when things seem to be proper, just to be sure).

Now, stones are another animal. Running one of these (as I ran, for grins,
a couple samples of Murchison, and Ls) in this mode gives COMPLETELY screwy
results. Running any rocky material in Alloy mode will indeed leave you with
EXCTLY what you describe (can merely tell Ni, for example is present but
the numbers will be meaningless). The program will tend to ?fill in? the
report for the elements it can?t see by drastically increasing the ones it can
see (so all the metallic elements, even if they only make up a small portion
of the sample, will add up to 100% in the final report). This is why I got
messed up results like Murchison having 60+% iron.

There is also (really commonly on these things from the factory) what is
called ?mining mode?. In this mode the machine will report the elements seen
(at least the ones ?turned on? for reporting) and a number roughly
coinciding with the size of the graph peak. The results in this mode is often (from
my goofing around with this mode anyway) relatively close to what the proper
mode would give and can be used for comparing one type meteorite to another
(for example, a CK might consistently give a higher reported result or a
certain element than a CV and both of those may be higher than a CM). As
such, you can gain some headway towards identifying different types using this
mode. HOWEVER ? THE ACTUAL NUMBERS GIVEN IN THIS MODE ARE NOT TO BE
CONSIDERED ACCURATE!!! To get the accurate numbers from those reported in this mode
would indeed require (just as you describe) a detailed certified lab analysis
to tweak them to accuracy. For some unknown reason, this mode is OFTEN the ?
second program? on these things from the factory (the Colorado Geologic
Survey had only this and alloy on their machine. I am really thinking that this
may be how yours was set up as well).

Stone meteorites should be run in what is referred to as ?SOILS MODE?.

It is true that the numbers for elements in concentrations well above 10%
may not be super accurate though. This mode is really for getting data on the
things in ppm concentrations. 10ppm = .0001% folks! There are indeed some
interferences that one (always) has to keep in mind, but these machines
should give quite accurate results for most stone (or soil) type samples (at
least for the majority of elements). This MUST be the case, or these things
would not be allowed to be used for such things as soil contaminate analysis by
the EPA (a MAJOR uses for these devices). I think the acceptable ?tolerances?
 for these uses is that it must be accurate to within 10 or 20% (in other
words, if it tells you you have .147% Ti in a sample, the certified lab
results must be between .125% and .170% or your XRF is considered to be out of
calibration ? assuming that is, that you have not overlooked an interference
issue).

The MANY meteorites I have run with this thing all come out quite close to
official lab analysis (for ones I have other lab results for) for most
elements. I was VERY surprised to see how close the data I have for the dozen or
so different Lunar anorthosites matched the data the Carl gave me for
Calcalong Creek (I can only compare to ?bulk? analysis data as that is what this
machine really does. Lots of lab data is for only particular minerals in a
meteorite and not the bulk). The numbers I am getting for most of the
elements (I had my machine custom programmed to be looking for elements in
meteorites that may allow me to sort them by type) have all been, for the most part,
very consistent and close to what little ?bulk analysis? data I have for
the same type meteorites.

Now, that being said, I do have some problems with crust and weathering.
The elements in crust have been oxygenated (and some volatilized and removed,
compared to an internal cut surface), so the numbers get a bit skewed. The
same goes for a natural weathered surface (those have the additional problem
that often other things have attached or leached in ? like Al, Ca, etc.) I
am trying to learn (by running hundreds of different samples) how to
compensate for these issues (and may, ultimately, not be successful in this,
unfortunately).

Any way, I have spent a couple valuable hours typing all of this (I have
dozens of L and H chondrites waiting for analysis, and I need to pack for my
trip) and need to move on. Some of what you say is indeed true, but much
leads me to believe that you are attempting to use a machine that is NOT set up
correctly for the job. One of these days (Denver spring show time perhaps) I
would love to see what the School of Mines got for an XRF and have a look
at how is was set for them.

Thanks (everybody) for taking the time to read all of this and give it some
thought!

Blaine
Received on Tue 15 Mar 2011 05:20:22 PM PDT