[meteorite-list] Oriented Meteorites?

From: jason utas <jasonutas_at_meteoritecentral.com>
Date: Thu, 28 Feb 2013 22:40:20 -0800
Message-ID: <CAK837U0C3Xbj-odDWG-dm3Zw=DUL5PhavgNcO_kDApcnqiswAw_at_mail.gmail.com>

Hello Brandon, All,
"Oriented" typically means that it is evident that a stone attained
stable flight for at least the later portion of a given meteorite's
ablative time spent falling to Earth.

However, this sort of thing can be somewhat subjective, and it is a
greyscale ranging from "not at all oriented" to "very much so."

Not so much [shield-shaped, minor froth on trailing face]:

http://www.fallsandfinds.com/attachments/Image/Katol/complete/72.678/DSCN2719.jpeg
http://www.fallsandfinds.com/attachments/Image/Katol/complete/72.678/DSCN2717.jpeg
http://www.fallsandfinds.com/attachments/Image/Katol/complete/72.678/DSCN2714.jpeg

Very much so:

http://www.fallsandfinds.com/page9.php

Generally, if a meteorite's crust shows flow-lines, I'll call it
flight-marked. If it has a shape that denotes stable aerodynamic
flight, then it's at least somewhat "oriented."

But many sellers don't seem to be able to tell the difference between
"oriented" meteorites and:

1) Broken stones, especially if sand-blasted. If you take a round,
fusion-crusted stone and break it in half, you get a "heat-shield"
shape. But not an oriented stone. Especially common with NWA's.
Corner chips off of larger stones often exhibit convex surface of
crust and concave broken faces.

2) Fusion crusted stones that show no sign of orientation, but are
shaped kind of like a heat-shield. Similar to above, but atmospheric
break. The broken face fuses over, and an "oriented" shape results.
But, no flow lines or evidence of lipping or thicker crust on trailing
face of stone.

3) Stones that show vague traces of orientation, if any. Sometimes, a
dealer calls a meteorite oriented and...I just don't get it.

Not much else to say...it really is a greyscale, and, while I wouldn't
call "orientation" subjective, someone else might deem flow-lines
enough evidence to call something "oriented," regardless of shape.

Regards,
Jason


> From: Brandon D. <b1dunovant at aol.com>
> Date: Thu, Feb 28, 2013 at 6:04 PM
> Subject: [meteorite-list] Oriented Meteorites?
> To: meteorite-list at meteoritecentral.com
>
>
> Hello Everyone,
>
> I have a question I'm sure can be answered here to my satisfaction.
>
> What defines an "Oriented meteorite"? I've noticed a trend starting where
> people have begun calling any meteorite with a rounded edge oriented or
> "slightly oriented".
>
> What truly defines an oriented meteorite? I have dozens of shields with
> radial flowlines and bullet shaped stones and irons, so I see orientation,
> but what's the true criteria?
>
> Thank you ahead for any replies.
>
> Best,
> Brandon D.
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Received on Fri 01 Mar 2013 01:40:20 AM PST