[meteorite-list] getting oriented on orientation

From: Dave Gheesling <dave_at_meteoritecentral.com>
Date: Wed, 5 Mar 2008 15:23:19 -0500
Message-ID: <203A1CAF064A4AE2BFBF07D442DAE2AD_at_meteorroom>

Steve & List,

I just sent the following to Darryl off line, as we've been discussing this
issue with great interest, and thought I'd add it here because it
coincidentally makes very similar points (we very much agree) but with
perhaps a little different perspective:

Darryl,

Here are the problems, in my opinion, with the simplicity of that 0-1-2-3
formula:

First, freshness of the specimen can have a lot to do with several of the
parameters, and just because a stone is weathered does not mean it's
necessarily not "completely oriented."

Second, a specimen's flight can be "completely oriented" but, due to the
initial shape and composition of the meteoroid, it might not be a perfect
nose cone. Frankly, again in my opinion, the object of much debate
yesterday is "completely oriented" but was affected by these parameters
(meaning largely by the second point and slightly by the first point, as it
is very fresh but was obviously not picked up the day it fell). If you
missed the extra photos, check this out:

http://www.fallingrocks.com/Collections/NWAXXXb.htm

I don't care what the final analysis is on this specimen, by the way, and am
only using it as a frame of reference. If you saw that Kainsaz specimen
(will link it below as well), even it introduces some interesting challenges
to the "current working formula" though it is obviously "completely
oriented":

http://www.fallingrocks.com/Collections/Kainsaz.htm

How one would provide for differentiation between this Kainsaz and, say,
Lafayette based on a "completely" or "partially" oriented grading system, I
am not sure. Layfayette is obviously fresher, has all sorts of flow lines
and is a perfect dome, but they are both "completely oriented" in terms of
flight and the resultant shape they both achieved.

This will be fun to sort out, and I hope we get it to the finish line!

Dave


-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of
MeteorHntr at aol.com
Sent: Wednesday, March 05, 2008 3:17 PM
To: fuzzfoot at comcast.net; darryl at dof3.com;
meteorite-list at meteoritecentral.com
Subject: Re: [meteorite-list] getting oriented on orientation

Hello Mike and all,

Mike, I like your suggestion.

Obviously, a large contributing factor in a the final shape of a meteorite,

has to do with it's original shape of the rock before the fireball (or as
it
broke apart in flight). Some rocks are just destined to look better (more
nosecone or shielded in shape) than others. But that gets more into
subjective
interpretation.

One challenge is that composition and weathering can play a part in the
appearance of a meteorite.

The Brenham Main Mass, while few would argue is not oriented, does not have

flow lines, or a roll over lip. The trailing side is noticeably more rough

than the nosecone, as it was not melted, but there is not "frothy" evidence
of
bubbling on in the low pressure zones on the back side.

So, while it would not have ALL 5 or 6 or 7 or 8 potential characteristics
of being oriented, the evidence points that it indeed was 100% oriented in
it's flight, thus producing the shape it is in now, less a bit of
wathering.
Also, I am not sure that a large pallasite would have the same ability as a

Eucrite would have in displaying the different potential characteristics?

So would the Big Brenham get a "lower grade" than a strange shaped
Millbillillie that might have more characteristics, yet not look even close
to what
one thinks an oriented meteorite should be?

I think there are some characteristics that lead to a definite conclusion
that the rock did not tumble in flight.

I think if a dealer, or collector wants to represent their meteorite
specimen as oriented, they need to justify why they think it is, base on
the
accepted criteria. Then it is up to the observer/buyer to evaluate the
quality of
those characteristics.

Not all flowlines are the same. Not all roll over lips are the same. Not
all frothy crust on the trailing side is the same. Not all curvature of
leading edge is the same.

Are we going to then grade each charateristic on a scale of 1 to 5?

A description might then look like this.

"Based on the "IMCA 4-Point Scale of Orientation' this rock grades at a
2.25
out of 5 as follows:
Characteristic A: Flowlines Scale 1-5 = 4 note: flowlines over 60% of the

rock All from a radiant point
Characteristic B: Roll Over Lip Scale 1-5 = 2 note: Mild roll over lip on

25% of the edge
Characteristic C: Parabolic Curve Scale 1-5 = 3 note: curvature is on a
280*
curve on X axis, 264* on Y axis
Characteristic D: Bubbling trailing side Scale 1-5 = 1 somewhat different
texture on the back side
Total 4+2+3+1 = 9 / 4 = 2.25"

Or, you do like Mike Farmer mentioned, you call it oriented, and you supply

16 photographs to back up your point.

Or, you say, like Mike suggested: O3, O2 or O1, Completely, Partially, or
Some, and justify why.

My two flowlines worth.

Maybe we should set up a Crater grading scale while we are at it?

Steve Arnold
Arkansas




.
In a message dated 3/5/2008 11:17:41 A.M. Central Standard Time,
fuzzfoot at comcast.net writes:
Great suggestions, Darryl. I would go even a little less complicated and
suggest a 3 number rating system. Here are some quick, nut-shell
definitions:

O3 - Completely oriented: Obvious and conclusive evidence that the
meteorite
stabilized during entire flight.

O2 - Partially Oriented: Evidence that the meteorite stabilized during most

of flight, but also tumbled of axis.

O1 - Some Orientation: Evidence that the meteorite stabilized briefly at
one
or several different points during flight, but tumbled majority of flight.

No Orientation - If no orientation is present, then there is probably no
need to mention it in description.

Other considerations: Where does 'dual orientation' fit in? I have had
numerous Sikhotes that have had 'bullets' or 'buttons' on both ends -
evidence
that the they flopped like a pancake and partially stabilized on both
opposing
edges.

Keep the suggestions coming.

Best,

Mike Bandli
www.Astro-Artifacts.com
 



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Received on Wed 05 Mar 2008 03:23:19 PM PST