[meteorite-list] New Iron

From: Impactika at aol.com <Impactika_at_meteoritecentral.com>
Date: Thu, 5 Apr 2007 19:29:49 EDT
Message-ID: <c97.c67b6bf.3346e06d_at_aol.com>

Forwarded for Robert Matson:
In a message dated 4/5/2007 3:23:32 P.M. Mountain Standard Time,
ROBERT.D.MATSON at saic.com writes:
Hi Anne,

Based on probabilities, one would assume an octahedrite of some type. The
principle spatial frequency in the upper right corner of the cut surface
to be around 2mm, though it isn?t clear to me whether these 2mm features are
indicative of taenite/kamacite boundaries (which would put it in the middle
the coarse octahedrite (Og) range), or something else. For now I?ll assume
the ~2mm basic frequency is showing lamellae boundaries, so the question
is which Og type?

Without knowing anything about the quantity of trace metals, it?s really not
possible to decide among IAB, IC, IIE, IIIAB, IIIE, IIIF or simply anomalous.
IC is very rare (and this iron doesn?t look like any IC?s I?ve seen), so I?
ll play
the percentages and exclude it. Similarly, IIE is rare, and I don?t see
anything that looks like silicate droplets, so I?ll drop it from contention.
IIIF is unlikely because of the high amount of schreibersite inclusions.
So I?m down to IAB, IIIAB, IIIE or anomalous.

It certainly ~looks~ anomalous, but that seems like a bit of a cop-out;
braver to choose an actual group. Going back to IAB, inclusions of
troilite [e.g. schreibersite] and cohenite (and graphite) are often abundant
in this group, so that?s a check mark in favor of this common group. IIIE?s
are abundant in carbide, which makes them a bitch to cut. Their bandwidth
is 1.2 - 1.6 mm, which seems a little smaller than what I?m seeing in the
image. Since no mention was made of cutting difficulty, it probably makes
sense to exclude IIIE.

IAB and IIIAB are the two most common iron meteorite groups, so it?s
pretty ?safe? to pick one or the other. I slightly favor IAB over IIIAB
IAB?s on average contain more trace elements, and the cut pattern looks
closer to IAB to me than IIIAB.

Final answer: IAB, Og

Best wishes,

Very interesting!!
Anyone keeping track of the bets?
Anne M. Black
IMPACTIKA at aol.com
President, I.M.C.A. Inc.

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Received on Thu 05 Apr 2007 07:29:49 PM PDT

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