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Tambo Quemado (IIIAB) - 80.60g Slice with Unusual Inclusion

Below are photos and comments from Bernd Pauli on a meteorite known as Tambo Quemado. Discovered in this slice is a very unusual inclusion which can be seen in the photos below. Bernd posted this description in an email to the Meteorite Central Mailing List which describes it very well. This specimen is part of the Bernd Pauli Collection.

Bernd Pauli: "Tambo Quemado, a member of the IIIAB irons that must have been artificially reheated to about 1000C at some point of its history and the result: fused schreibersite crystals and transformed kamacite grains are clearly visible under a microscope. The troilite nodule has a whopping diameter of 17 millimetres, has a mottled appearance and is surrounded by a seam of schreibersite.

It's an incredibly beautiful iron - see Martin Horejsi's and Marlin Cilz's article in the Meteorite Magazine, May 1998, Volume 4, No. 2, p. 13 or go to BUCHWALD V.F. (1975) Handbook of Iron Meteorites, Vol. 3, pp. 1174-1177.

When I closely inspected the troilite nodule under my microscope at 16x and at 32x magnification, I was "dumbfounded" when I found something that should not be there.

It is a "stony", maybe a silicate-related inclusion at the upper edge of the troilite nodule. Wondering what I was looking at, I searched for information both in O. Richard Norton's Encyclopedia, in Buchwald, and in McSween. On page 205 of "Meteorites and Their Parent Planets", Mc Sween says that "silicates in IIIAB irons are similar in composition to HED chondrites".

Now, my inclusion doesn't look like it could be of HED origin. Visually, it looks more like the Cumberland aubrite texture - a very improbable, unlikely provenance though.

Vagn Buchwald says that silicate inclusions in IIIAB irons are extremely rare and in Appendix I, pp. 152-153, he mentions only 2 irons that may be silicate-bearing: Avoca (olivine?) and Grant (tridymite, glass or silicates?)

In "Astronomy Now" for October 1996, p. 4, I found this:

Silicate inclusion is meteorite mystery

Type IIIA and IIIB iron meteorites are thought to have formed in the cores of asteroids. They often contain small inclusions of chromite and one or more iron-bearing phosphate minerals which probably formed in the late stages of core crystallisation. The recent discovery by American scientists of a silicate inclusion in a type IIIA meteorite Puente del Zacate is much harder to explain. According to the authors of the report in Science, "How a graphite-bearing silicate inclusion was introduced into a low-carbon IIIA iron core is difficult to envision." One possible answer is that the inclusion originated in the lower mantle of the asteroid close to its iron core. Another possibility is that some small masses of iron formed and cooled inside the silicate-rich mantle (by Peter Bond).

See also:

OLSEN E.J. et al. (1996) A silicate inclusion in Puente del Zacate, a IIIA iron meteorite (Science 273, 1365-1367)."

Note: These images are high quality and may take a couple of minutes to load.

Copyright  2004 - Bernd Pauli
Tambo Quemado (IIIAB) - Inclusion in 80.60g Slice

Copyright  2004 - Bernd Pauli
Tambo Quemado (IIIAB) - Inclusion in 80.60g Slice

Copyright  2004 - Eric Twelker (MeteoriteMarket.com)
Tambo Quemado (IIIAB) - Inclusion in 80.60g Slice

Magnified Image Details:

Tambo Quemado, (Photo 1)
Magnification: 16x
Exposure: 1/20
Eyepiece projection
Aperture: 6.7

Tambo Quemado, (Photo 2)
Magnification: 32x
Exposure: 1/25
Eyepiece projection
Aperture: 3.5


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