Hi Jeff and all!
I'd say XRF data can and does vary. Not enough info in the write up on
testing methods. What is the accepted procedure
agreed to using XRF to test? BIG QUESTION!
Read on!
A few years ago, XRF seemed to not be considered much in this
community. Only a few were using it pretty much only for determining if
a rock
had the attributes to be considered a meteorite. Somewhat like PIXE
tests. Some places have XRF, some have PIXE where they are looking for
key elements.
I know XRF technology has improved. I found it refreshing that the XRF
data was listed.
Correlations being standard methods of lab testing and XRF showed to be
0.85 to 0.95 (or there abouts) by the EPA in a paper about testing lead a
while back that I read. Calibration reference is key to accurate,
repeatable measurements with XRF.
In the gold and silver industry, they have been accepted widely but
generally on massed samples (by melt - Homogenous mixture).
My question about the XRF data is how was the measurement taken. It
stated whole rock and the mean of two shots??? So, does that mean
that the sample was massed and pressed into a disk then shot twice or
what? I'd love to know how this was performed.
Overall, with probe data, the XRF is somewhat redundant and without what
it was referenced to, eye candy, but very interesting.
Don't think XRF would take the place of probe data. Both can be
subjective to a point. It would be nice to read if the same standards
were used for
calibration for both the probe and XRF were used and the correlation.
I do think XRF can have it's place. Standard's should be developed on
how it might be used. Maybe they are out there. Point and shoot, if you
are looking
for a quantitative answer, is not the way IMHO.
Jim
On 12/31/2013 6:04 PM, Jeff Grossman wrote:
Can't resist doing some arm-chair science... usually a bad move, but
oh well... I'll probably end up retracting much of this speculation...
There IS something strange about this meteorite to me. I don't know
how good the XRF analysis is, but it is not what I would expect from
an L chondrite. These analyses show a 30-40% enrichment in Ca and Al
relative to Si over what an L chondrite should be, and siderophiles
are ~20% too high as well. If these are accurate, then there has been
fractionation, suggestive of enrichment in low-melting components
(which is odd). Sodium does not fit this story, but it's a harder
element to analyze by xrf. I also agree that coarse poikilitic grains
are hard to explain by solid-state metamorpism, but they could also be
derived from relict chondrules. If this rock was melted to a large
extent, I'd expect it to be depleted in metal and sulfide. So I'm
betting that the whole system has experienced low-degree partial
melting, and some of these melts have infiltrated this particular
chunk of high-metamorphic-grade L chondrite.
I agree with Carl that this has hallmarks of what many people call a
type 7 chondrite. But the whole issue of how to draw lines (or if
there ARE lines) between primitive achondrites, type 7 chondrites, and
products of shock heating/melting is very fuzzy and tends to be highly
interpretive. In a sense, this is the same discussion that surrounds
Portales Valley, an ordinary chondrite that has also "been around the
block."
Here is an article on Katol that Laurence Garvie pointed me to:
http://www.geosocindia.org/abstracts/2013/feb/p151-157.pdf
Jeff
--
Jim Wooddell
jim.woodd...@suddenlink.net
http://pages.suddenlink.net/chondrule/
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