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Re: Monahans

David Weir schrieb:

> Bernd and list,
> I have been seeking to aquire a IIF specimen for my collection for
> some
> time and Monahans (1938) is classified as such in the British Catalog.
>
> Any information regarding this meteorite and its whereabouts would be
> gratefully appreciated.
> David

Hello David, hello List!

There is one problem about the IIF classification of Monahans (1938).
Although the 4th edition of the British Catalog of Meteorites does list
5 IIF plessitic irons (Corowa, Del Rio, Dorofeevka, Monahans (1938),
Repeev Khutor), there is no such group - neither in Frank Stroik’s
posting ‘Iron Meteorite Classification: Part I’ (Sun, 23 Mar 1997
16:25), nor in my database (no Antarctic, no non-Antarctic IIF irons),
nor does Buchwald mention any IIF irons (and Wasson doesn’t either).
There are 6 IIIF irons but they have a considerably lower Ni content
(6.6-7.9% Ni). There are even further inconsistencies:
Whereas Corowa, Dorofeevka, Monahans (1938), and Repeev Khutor are
listed as plessitic octahedrites, Del Rio is listed as a nickel-rich
ataxite (although Repeev Khutor has a higher nickel content).
The correlation of the gallium values is pretty good, whereas the
scatter between the germanium and iridium values is considerable.

Corowa ------ 13.40 %Ni -- 10.1 ppm.Ga -- 159 ppm.Ge -- 0.77 ppm.Ir
---------------- 13.13 %Ni

Del Rio ------ 11.34 %Ni -- 9.19 ppm.Ga -- 98.6 ppm.Ge -- 19 ppm.Ir
Dorofeevka - 11.57 %Ni -- 9.10 ppm.Ga, 124 ppm.Ge, 23 ppm.Ir
---------------  11.26 %Ni

Monahans ---10.88 %Ni -- 8.9 ppm.Ga -- 127 ppm.Ge --14 ppm.Ir
--------------- 10.60 %Ni
----------------- 4.99 %NiO

Repeev Kh. - 14.30 %Ni -- 11.6 ppm.Ga -- 193 ppm.Ge -- 3.0 ppm.Ir

No wonder, then, that these 5 meteorites are grouped as anomalous.
Should someone have background information about the IIF classification,
I’d really appreciate hearing about that.

The 3rd edition of the British Catalog (1966) has the following entries:

Corowa => Nickel-rich ataxite
Del Rio =>  No entry
Dorofeevka => Medium octahedrite
Monahans => Nickel-rich ataxite
Repeev Kh. => Octahedrite

Appendix to the Catalog of Meteorites (1977):

Corowa => Plessitic octahedrite; chemically anomalous
Dorofeevka => Plessitic octahedrite (0.09 mm); chemically anomalous
Monahans => Plessitic octahedrite; chemically anomalous
Repeev Kh. => chemically anomalous

Best wishes, Bernd

P.S.: Monahans (1938), its whereabouts

1.2kg, Tempe, Arizona State Univ.
901g, Fort Worth, Texas, Monnig Colln.
873g, Washington, U.S. Nat. Mus.
844g, Chicago, Field Mus. Nat. Hist.
811g, Harvard Univ., BM London
5325g (and fragments, 217g and sawings, 168g).

P.S.S.: No one seems to have responded to Alexander Seidel's Guadalupe y
Calvo question yet (see Hexahedrite posting). Does nobody have a GyC
slice that she or he could describe? Are there Neumann lines clearly
visible? Does it have a 'cloudy' texture?
Follow-Ups: References: