[meteorite-list] FRANCONIA

From: Melinda Hutson <mhutson_at_meteoritecentral.com>
Date: Thu, 2 May 2013 18:28:53 -0700
Message-ID: <CANP=7y_jjYbnWUYJXa-TinqDLhRQm43V1_DULW1dgC0PMV1suA_at_mail.gmail.com>

It has been interesting reading some of the posts that have come to my
attention. I thought I would take the time to answer this one.

Regarding the following:
"One more question regarding the latest Franconia paper, M. Hutson et
al., 2013, regarding the sample sized used in that study vs. their
concluded number of falls for the area: They only looked at 14 rocks,
concluding that 7 were separate falls. If they looked at 50 rocks,
would they have found 25 falls? Why did they select only 14 rocks,
was it a matter of how much research they could fund? I'd hope the
samples were not selected specifically for their appearance, as they
stated in the paper that visual pairing based on the exterior of the
stones was completely misleading."

If one reads our paper carefully, you will find the following
statement "The Cascadia Meteorite Laboratory (CML) received samples of
12 unclassified chondrites over a 6 year period. These samples were
obtained from different people in a non-coordinated fashion." That
means that material came in at random. We never planned to study the
Franconia area, and it would be impossible to get grant funding to do
so (I've discussed this with Laurence Garvie at ASU--grants fund
well-defined research projects that have a focussed goal. No one
funds classification of meteorites). Our lab does a small number of
classifications as "side projects" using whatever money we can raise
from the public. We have an annual fundraiser, which provides most of
our budget for the year. We have a huge backlog of unclassified
material, and prioritize based on a variety of criteria, including
whether a sample looks interesting and might lead to a grant funded
project. In the case of Franconia, the first sample I got was Buck
Mountain Wash, from Larry Sloan, who was very generous in providing
material. Digging into this stone led to a paper:

Hutson M., A. Ruzicka, R. Pugh, L. Sloan and E. Thompson (2007)
Complex brecciation and shock effects in the Buck Mountain Wash (H3-5)
chondrite. Meteorit. Planet. Sci. 42,
963-978.

In addition to the 12 meteorites that came in, we looked at one thin
section from ASU (at their request) to see if it paired with one of
ours, and we examined a piece of the original Franconia meteorite (in
order to compare all of the H chondrites we were seeing to the
"original"). It became clear that there were several different H- and
L- chondrites, and that Buck Mountain Wash was extremely variable. At
that point, I decided to get terrestrial ages to confirm or refute
what the petrology and chemistry seemed to be telling me. This
project spanned years, and used up a fair amount of our public
donations for thin section preparation (over two dozen sections were
prepared), time on microprobes (our university doesn't have one--we
used 3 different ones at two other universities), time on scanning
electron microscopes (our old one and our new one). None of this was
free.

Nor are we done. BM 005 has an interesting complex shock melt dike,
which will lead to a paper (the LPSC abstract and poster are on-line,
A Pyroxene-Enriched Shock Melt Dike in the Buck Mountains 005 (L6)
Chondrite M. Hutson, A. Ruzicka, R. Brown 44th Lunar and Planetary
Science Conference (2013), Abstract #1186 ). We also have a number of
additional stones that have come in to the lab and are awaiting study.
 We would like to get terrestrial ages on all of these, BUT, we don't
have enough funds (for pricing, check out
http://www.physics.arizona.edu/ams/service/fee.htm--we are under the
category of nonprofits, but not NSF).

Regarding:
"They incorrectly reported that the 14 stones in their study make up
3.7% of the total finds for the area, 380. We all know this number is
much higher, by a factor of 20 or more probably. For example, I know of
one hunter who made more than 600 finds in a single year. A similar
disconnect exists with their statement regarding the % representation of
total mass of all finds. I'm not sure how they can come to such a
definitive fall count with such a miniscule sampling of finds from the
area."

The numbers are correct for Smaller's data set. Which is the only
data set we had to work with. We admit in the paper that this is an
underrepresentation of what is actually out there. But you can only
work with the data that you have. Trying to speculate on how much
higher is the number/mass is just that: speculation.

Regarding:
"Ok, two questions: Does anyone know why the irons (H-metal) from the
area were ignored in this study? Surely they are directly related to
these chondritic falls, and as Yucca 015
(http://www.lpi.usra.edu/meteor/metbull.php?code=57175) shows us,
there are multiple unique H-metals out there as well."

Studying metal/irons requires different equipment (such as neutron
activation or LA-ICPMS) than studying stones (EMP, SEM, petrographic
microscope). Our lab doesn't have that equipment. The only LA-ICPMS
that we have access to in Oregon (at another university) does not have
standards needed to analyze metal.

If you are interested in learning about our lab, please read our
August 2012 newsletter (http://meteorites.pdx.edu/news-CML.html),
which describes the activities of our lab, including the larger number
of projects supported by public donations. You will be surprised at
how small our yearly budget is. We pinch pennies 'til they scream to
get as much information as we can. Most of our individual donations
are $50-$100. We would greatly appreciate ANY support from anyone on
this list.

Melinda Hutson
Received on Thu 02 May 2013 09:28:53 PM PDT