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Re: Mind your F's and E's

David Weir schrieb:

> Matt and list,
> I'll try to help out with your question on kamacite bandwidth
> structures
> most common in IIE, IIF, IIIE, and IIIF classifications. My source is
> from the series of articles in GCA on the chemical classification of
> iron meteorites by Wasson et al.
>
> The IIE structure determined in 12 members of that class have widely
> varying bandwidths from 0.1 to 2.0 mm and is uncorrelated with Ni
> content. This would include structures from fine to coarse. Some
> members
> in this group have silicate inclusions and some are devoid of all
> silicates. A nonigneous origin is favored within impact-produced melt
> pools deep down. Structure was not relied on to differentiate this
> group.
>
> The IIF structure found in 5 members of this class exhibits an
> increasing bandwidth for an increasing Ni content, the opposite of
> what
> usually happens with slow cooling. Two groupings of bandwidths are
> found; a) 0.05 to 0.09 mm, and b) 0.20 to 0.21, the majority
> displaying
> a plessitic structure. A close relationship between this group and the
>
> Eagle Station pallasites has been proposed.
>
> The IIIE members have bandwidths in the range of 1.2 to 1.6 mm for a
> medium to coarse structure with a majority being coarse. The parent
> body
> has close affinities to the IIIAB parent body but a split was made
> based
> primarily on the IIIE's abundance of carbide.
>
> The IIIF members define a small but unique class whose structure
> displays bandwidths from 0.5 to 1.5mm, with much higher bandwidths up
> to
> 10 mm originating after cooling, and displaying a medium (St.
> Genevieve
> County, Moonbi) to coarsest (Nelson County) structure.
>
> Good research provoking question. Hope this helps.
> David

Hello David, hello List!

Thank you, David, for these interesting details. Here's some more:

IIE Irons:

1) According to Wasson, Mont Dieu is an ungrouped iron, with 7.55 wt% Ni
content, but Meteoritics 32-Suppl. 1997, July, Met.Bull 81, p. A161
lists Mont Dieu as a IIE iron which would bring the total of IIE’s to
16.
2) V.F. Buchwald, R.S.Clarke, Jr. (1987) The Verkhne Dnieprovsk iron
meteorite specimens in the Vienna Collection and the confusion of
Verkhne Dnieprovsk with Augustinovska (Meteoritics 22-2, 1987, 121-135):
Verkhne Dnieprovsk is even classified as a finest octahedrite with a
bandwidth of only (0.07 ± 0.02 mm) in its undistorted areas.

IIF irons: Buchwald speaks of  ‘(kamacite) spindles’ in a Widmannstätten
pattern.

IIIE irons: Burlington - Cachiyuyal - Colonia Obrera - Coopertown -
Kokstad - Paloduro - Paneth's Iron - Rhine Villa - Staunton - Tanokami
Mountain - Willow Creek - Xinjiang / Nickel content 7.88 - 9.66
Paneth's Iron, for example, contains the carbide haxonite = [( Fe, Ni,
Co)23C6].

IIIF irons: Clark County - Klamath Falls - Moonbi - Nelson County -
Oakley - St. Genevieve County /Nickel range: 6.6 - 7.9

Regards, Bernd
References: