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Re: I need help

Frank Stroik schrieb:

> I was wondering if anybody out there has a post I did for list a while
> back, entitled "Understanding Iron Meteorites". I have tried to access
> Meteorite central, but we all know that this is futile. If you can
> e-mail it to me directly that would be great. Thanks, Frank

These posts were so informative that we should give them to all list
members once more. There are quite a few new members who will surely
appreciate the quality of these contributions!

I have also added some of the other posts we exchanged last March. I
hope you don't mind. If you do, there is a delete button :-)

------------ snip ------------

01) From: fes@UWYO.EDU
Date: Sun, 23 Mar 1997 16:25:10 -0700 (MST)

Iron Meteorite Classification: Part I

Perhaps the most complicated, and least understood classification system
in science today (with the possible exception of crinoid classification
in paleontology) is iron meteorite classification. I have spoken to a
few researchers, and few understand it completely. I am going to try to
explain it so that when you visit a museum, read a book, or perhaps look
at your own specimens, you will be able to realize what exactly the iron
meteorite is telling you.
First a knowledge of the minerals kamacite and taenite is needed to
understand the Widmannst,tten structure. By understanding this you will
be able to tell how hot the meteorite was, and how long it took to cool.
If you have slice of an iron meteorite, go get it and refer to it as you
read this, as it always helps to look at what someone is writing about.
Kamacite and taenite are minerals that compose the majority of  iron
meteorites. They are formed by cooling of a magma (molten material).
In this case the magma is composed mostly of two elements iron (Fe) and
nickel (Ni). As the magma cools, these elements begin to bond together.
The definition of the Widmannst,tten structure is as follows: The true
Widmannst,tten structure forms by a diffusion-controlled nucleation that
is slow, even on a geologic time scale (Buchwald 1975). What does this
mean? In simpler terms, it means it takes a long time to cool Fe and Ni,
and even longer to bond them together. It is the amount of time for
cooling that generates the size of the bands in the Widmannst,tten
structure. Ni would like to bond as soon as possible. At about 1100oC,
Ni atomic stucture is stable enough to allow bonding. Fe however is
still reluctant to bond. So as time passes more Ni atoms bond than Fe
atoms bond. This continues until most of the Ni is gone from the melt.
Now here is an implication for the different types of iron meteorites.
Since it is generally accepted that iron meteorites are derived from an
asteroid core, this allows us to model a planetary core in some detail.
In doing this, it gives us a look at how the Widmannst,tten structure
clues us in on where a particular meteorite formed.
Ataxites are iron meteorites without structures. These formed first in a
melt, as they are composed of mostly Ni in their mineralogy.
Did you see the other connection? The more Ni you have the smaller the
Widmannst,tten structure until finally, it is no longer visible to the
naked eye. Ataxites are composed mostly of the mineral taenite, which is
rich in Ni, and demonstrate what an outer core of a planet must look
like.
On the other end of the spectrum we have Hexahedrites. These are
composed mostly of the mineral kamacite, which is the Fe rich
counterpart to taenite. Hexahedrites are the last to cool, and they
represent the inner core of an asteroid, which can be extrapolated to
other planetary cores. These meteorites ar basicly one large
Widmannt,tten band.
The other iron meteorites fall somwhere in between these two extremes.
Remember this, the larger the band width, the longer it took to cool,
and the closer it is to the inner core. Here is where a structural
classification comes to play.
By measuring bandwidth in an iron meteorite, we can assign them to
particular classes. These classes are chemical in nature, and will be
discussed next time. Suffice to say, bandwidth is a function of chemical
classification, and the two are dependent of each other.
Bandwidths range from 0.006mm - 3.1mm in each type of meteorite, there
is a very small tolerance in the width . For example, the group IIIF has
a bandwidth of 1.3-1.6mm if it was any higher, or lower, it would
indicate a different group, or a possible anomalous structure.
I will continue to discuss this classification in more detail over the
next few days. If you have questions, e-mail me, and I will answer them.
In any case, I hope this will help those interested in iron meteorites.

Frank Stroik
Department of Geology
and Geophysics
The University of Wyoming

Reference:
Buchwald Vagn F. (1975) Handbook of  Iron Meteorites, Vol. 1, pp. 243,
UCLA Press, 1975)


Iron Meteorite Classification: Part II

Today I will discuss the chemical classification of iron meteorites. It
is based on a simple idea, but one that is hard to follow. After this
writing, I hope that everyone will be able to look at the number
designation of an iron group and be able to realize what it means. There
are twelve groups of iron meteorites. Each group has members that are
related to each other, but each group is NOT related to another group.
This will become more apparent later. These twelve groups are so divided
on the basis of bandwidths, the concentrations of the elements germanium
(Ge), gallium (Ga) and iridium (Ir), and the amount of Ni. These
features help best to distinguish between the major groups, because they
can be measured with some confidence, and read sufficiently different
between the groups.
The reason for the choice of elements to anaylze for, is due to the fact
that when, let's say Ge-Ni compositions are plotted on a simple graph, a
few groups overlap each other. But when you plot all three elements (Ga,
Ge, and Ir) each group has it's own area on the graph.
I could keep writing, but the above is the classification scheme in a
nut shell. I will put up a table that shows the major properties of  the
individual groups.

Group Number Width(mm) Ni% Ga(ppm) Ge(ppm)
IA 82 1.0-3.1 6.4-8.7 55-100 190-520
IB 8 .01-1.0 8.7-25 11-55 25-190
IC 10 <3 6.1-6.8 49-55 212-247
IIA 39 >50 5.3-5.7 57-62 170-185
IIB 13 5-15 5.7-6.4 46-59 107-183
IIC 7 0.06-0.07 9.3-11.5 37-39 88-114
IID 13 0.4-0.8 9.6-11.3 70-83 82-98
IIE 12 0.7-2 7.5-9.7 21-28 62-75
IIIA 120 0.9-1.3 7.1-9.3 17-23 32-47
IIIB 36 0.6-1.3 8.4-10.5 16-21 27-46
IIIC 7 0.2-0.4 10-13 11-27 8-70
IIID 5 0.01-0.05 16-23 1.5-5.2 1.4-4
IIIE 8 1.3-1.6 8.2-9.0 17-19 34-37
IIIF 5 0.5-1.5 6.8-7.8 6.3-7.2 0.7-1.1
IVA 40 0.25-0.45 7.4-9.4 1.6-2.4 0.09-0.14
IVB 11 0.006-0.03 16-26 0.17-0.27 0.03-0.07

Table based on Scott (1975) table 2.
Ir was not considered above, because it is such a small amount,
measuring with any accuracy is difficult. Still today, Ir is difficult
to measure, so I did not want to give information that may or may not be
right.
Now you can see what the term fine and coarse octahedrite means. Coarse
and fine relate to band width. Octahedrite refers to the crystal
structure of the Ni and Fe. It is basicly a cube. The next time I write
I will take a brief look at the different groups, and how they are
related to asteroids.

Frank Stroik, University Of Wyoming

Reference: Scott E.R.D. and Wasson J.T. (1975) Classification and
Properties of Iron Meteorites (Reviews of Geophysics and Space Physics
13-4,  pp. 527-546.


1) Re: Iron Meteorite Classification. Part I (/Mar97/msg00049.html)
2) Re: Iron Meteorite Classification. Part II (/Mar97/msg00066.html)
3) Re: Iron Meteorite Classification. Part II (/Mar97/msg00067.html)
4) Re: Iron Meteorite Classification. Part I (REPOST)
(/Mar97/msg00068.html)

02) Betreff: Mind your F's and E's
Zur?ckgesendet-Datum: Fri, 3 Apr 1998 11:42:55 -0500 (EST)
Datum: Fri, 03 Apr 1998 11:42:33 -0500
Von: David Weir 
An: Matt Morgan 

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.

03) Betreff: Mind your F's and E's
Datum: Fri, 03 Apr 1998 21:02:17 +0200
An: dweir@bellsouth.net
CC: Matt Morgan ,
meteorite-list@meteoritecentral.com

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 Widmannst,tten
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

04) Betreff: Iron classification chat
Zur?ckgesendet-Datum: Fri, 3 Apr 1998 15:40:46 -0500 (EST)
Datum: Fri, 03 Apr 1998 13:48:02 -0700
Von: Matt Morgan 

Hi List:
I have been researching iron meteorites for my book on Colorado
meteorites. In the process I made a chart of the roman numeral "symbol"
and how that relates to structural class. This was done with the help of
Buchwald and the "Blue Book" last evening. NOTE: This is general,
but is a neat quick reference.

Symbol -Structural Class

I -Coarse inclusion-rich octahedrites
I-An -Inclusion-rich irons
IIA- Hexahedrites
IIB- Coarsest Octahedrites
IIC- Plessitic Octahedrites
IID- Medium Octahedrites (10-11.5% Ni)
IIE- Fine-Coarse Octahedrites with Neumann lines common
(6.8-9.7% Ni)
IIF- Plessitic Octahedrites, Ataxites (10.8-14.3% Ni)
IIIA- Medium Octahedrites (7-8.8% Ni)
IIIB- Medium Octahedrites (8.6-10.6% Ni)
IIIC- Fine Octahedrites
IIID- Finest Octahedrites
IIIE- Coarse Octahedrites
IIIF- Medium - Coarse Octahedrites (7.0-7.98% Ni)
IVA- Fine Octahedrites (7.5-10% Ni)
IVB- Ataxites
ANOM -- Anomalous irons

05) Betreff: Meteorite Classification
Zur?ckgesendet-Datum: Mon, 6 Apr 1998 22:24:18 -0400 (EDT)
Datum: Tue, 07 Apr 98 05:31:42 GMT
Von: ALMitt@kconline.com

After Matt Morgan's excellent post on the Iron Classes I dug up the
classification chart I have been using curtesy of Phil Bagnall's book
"The Meteorite and Tektite Collectors Handbook. I Contacted Phil (a
frequent visitor here) and requested to post the classification I have
been using by his permission. Phil was very generous and gave me the new
second edition that will
be published in the second addition of his handbook now being published
and perhaps printing by William-Bell Inc. (also an excellent source of
astronomy publications) Enjoy the chart.

Meteorite Classification System

STONES:
Chondrites Carbonaceous CC
 Ivuna-type CI1
 Mighei-type CM2
 Ornans-type CO3
 Vigarano-type CV3
 Renazzo-type CR4
 Karoonda-type CK3-6
 Enstatite E
 H EH3-EH4
 L EL5-EL6
 Rumuruti R3-R6
 Acapulcoite A
 Ordinary:  OC
 H H3-H7
 L L3-L7
 LL LL3-LL7
Achondrites Angrite ACANOM
 Aubrites AUB
 Brachinites ABRA
 Ureilites AURE

 HED Sub-group:
 1) Howardites AHOW
 2) Eucrites AEUC
 3) Diogenites ADIO

 SNC Sub-group:
 1) Shergottites AEUC
 2) Nakhlites ACANOM
 3) Chassignite ACANOM

STONY-IRONS:
 Lodranites LOD
 Mesosiderites MES
 Pallasites PAL
 Siderophyre IVA-ANOM

IRONS:
 Hexahedrites H
 Octahedrites O
 Coarsest Ogg
 Coarse Og
 Medium Om
 Fine Of
 Finest Off
 Ataxites D


Courtesy of: Phil Bagnall in "The Meteorite & Tektite Collector's
Handbook" Willmann-Bell Inc, Second Addition (in press?)

03) Betreff: Meteorite Classification
Zur?ckgesendet-Datum: Tue, 7 Apr 1998 08:34:08 -0400 (EDT)
Datum: Tue, 07 Apr 1998 14:02:22 +0200

Hello Matt, hello Al, hello List!

For those among us who do not speak German:

The abbreviations used for the classification of iron meteorites like
Ogg, Og, etc. go back to the Rose-Tschermak-Brezina classification
scheme and stand for g = grob (= coarse) and gg = ganz grob (=
quite/very coarse). The D for ataxaites comes from German 'dicht' =
dense.

Gustav Rose (1798-1873) was a German scientist who introduced a
classification system in 1863 that became quite popular and was based on
mineralogy and composition.

Gustav Tschermak (1836-1927) was an Austrian (a native of Litovia,
Moravia = a former province of Austria) who modified Rose's system in
1872 and once more in 1883. His classification criteria were basically
petrographic.
Those famous 'double pyramid' sketches showing the Widmanst,tten
structure are by Tschermak.

Aristides Brezina (1848-1909), also Austrian, enlarged his predecessors'
schemes but somehow overdid it. He had, for example, 32 chondrite groups
(differentiated by color, texture, etc.).

Both Tschermak and Brezina (the latter studied under G. Rose) were
custodians of the Vienna mineral collection.

For more detailed information, see John G. Burke (1986) Cosmic Debris,
Meteorites in History, an excellent source for historical information.

Regards, Bernd

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