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Re: Mind your F's and E's
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
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