[meteorite-list] NWA 2677 Iron Meteorite, continued...

From: MARK BOSTICK <thebigcollector_at_meteoritecentral.com>
Date: Sun Dec 12 12:34:05 2004
Message-ID: <BAY4-F925ADF1166013C6BD3A4AB3AA0_at_phx.gbl>

Hello list,

I received an e-mail privately that corrects me on my "fine octahedrite"
analysis. Since this does not have any private information in it and I
imagine irons confuse other list members a little I will answer the e-mail
to the list, and attach the body of that e-mail below. Thanks for your
note. I guess I just thought fine as there was so much of the structure
visible on the small, 5g. slice. (I hear Ronald Reagan in my heat telling
me, "Mark, your no John Wasson.")

When I think of course octahedrites, I think of patterns like Toluca and
Nantan, which seem to me to have large crystalline structures.

Martin noted: Intersting to me, that some lamellae in that slice are
somewhat twisted from mechanical stress as one can find in many irons of
large tkw, which broke up. Gibeon, Henbury and of course from most crater
builders. So I would bet, that there are many more specimens still to be
found in desert...."

I did find the warped lamellae plates of interest and was what talked me
into getting a piece. I have a Gibeon and a Henbury slice showing these
features. In the case of these meteorites, and say like Canyon Diablo,
should we give credit to finding the warped lamellac plates to large iron
meteorites, or is this just a fairly common aspect. What I mean is, cut up
and etch enough of any one iron and you are sure to find some, perhaps?

I do not imagine a 100g iron by itself could create enough speed in falling
to warp any or the crystal plates. But it seems to me that features such
as, are likely to happen in space in the astroid belt..

Clear Skies,
Mark Bostick
www.meteoritearticles.com



According to Robert Hutchison book "METEORITES a Petrologic, chemical and
Isotopic Synthesis" page 333, published 2004:

"This work initially led to a splitting of four groups. For example, group
IV became subdivided into the genetically distinct groups IVA and IVB, the
latter having Ga and Ge contents well below the detection limits of Lovering
et al. (1957). Group III was split into six: IIIA, IIIB, IIIC, IIID, IIIE,
and IIIF. But analysis of increased numbers of meteorites led to a closing
of compositional gaps between groups and splitting was replaced by
combining. Groups IIIA and IIIB were recognized as one, group IIIAB. Not
only were groups IIIC and IIID recognized as one, they later recognized as
part of an enlarge group IA and IB, known as IAB. Choi et al. (1995)
recommend that the combined group be known as IAB, that "group IIICD" should
effectively be dropped. What was originally group III has become the
genetically distinct groups IIIAB, IIIE, and IIIF, with reassignment of some
founding members to group IAB."

"There are 12 groups of irons and the members of each are considered to be
genetically related." IAB, IC, IIAB, IIC, IID, IIE, IIF, IIIAB, IIIE, IIIF,
IVA and IVB. In table 10.1 he gives a nickel content for IAB as "Ni
6.5-60.8 wt%" and a bandwidth for IAB as "Og-D" - D being ataxite. On page
331, he gives the following bandwidth for Og " Coarse octahedrite (Og)
......... 3.3 -1.3 mm.

I interpret the about to mean that your NWA 2677 is a IAB Coarse octahedrite
(Og).
Received on Sun 12 Dec 2004 12:33:34 PM PST