Hallo Forum,
Die Untersuchung des Steines hat ausgewiesen das es sich um einen irdischen Basalten handelt.
Kein Meteorit also…
Da man von „Fehler“ lernen kann, will ich auch trotzdem hier die Resultate zeigen.
Jérôme Gattacceca von CEREGE (CNRS / University of Aix-Marseille) in Frankreich, der so freundlich war der Stein für mich zu untersuchen, hat mir genehmigt seine Resultate hier mit euch zu teilen.
Als erste gab es Resultaten von magnetische Tests:
I have checked the magnetic properties of your stone.
It contains only stochiometric magnetite, in a rather large amount.
The only match with a meteorite would be a nakhlite, although they usually
contain titanomagnetite rather than magnetite, and the magnetite
concentration is rather higher than usual nakhlites.
My first guess is that it is not a meteorite.
Anyway I will do a polished section and have a closer look.
Später erklärte Jérôme mir den Unterschied zwischen „stoichiometric-“ und „titanomagnetite“:
What I call "stoichiometric" magnetite is Fe3O4, without substitution of Fe by other elements.
The classical subsitution with magnetite is to have some titanium replacing some iron, which gives Fe(3-x)Ti(x)O4 (titanomagnetite).
The cool thing is that the Curie temperature (Tc) of titanomagnetite (i.e. the temperature above which the mineral is not magnetic any more) depends on the x value.
So a simple magnetic measurement vs temperature can tell you if you have Fe3O4 (Tc=585 °C), or titanomagnetite (Tc=575-552,7*x-213,3*x^2).
With the polished section I can have a better idea of the texture of the rock, compare that with other nakhlites, and possibly make a microprobe analysis (in October) if I still have a doubt.
Der Dünnschliff zeigte dann:
I had a look at the polished section today.
To me it looks like a terrestrial crystalline rock with a lot of nice magnetite crystals (I will send a picture on Monday). However, I will send the polished section to my colleague Albert Jambon in Paris. He knows much more than me about achondrites and will confirm what this is.
Und dann die finale Antwort nach seinen Besuch an Paris:
I am just back from Paris where I was doing microprobe analyses.
We had a look at your stone with Albert Jambon, and there is no doubt for him : it is a terrestrial rock of the basalt family.
In view of the high magnetite content, and texture, my only hope was it could be a nakhlite, but Albert Jambon showed me a few nakhlites and they look really different.
I attach a nice SEM image (backscatter mode : lighter colors = heavier elements, mostly controled by iron content here) of the polised section.
It shows :
- zoned pyroxenes (bright minerals, with core slightly darker because less iron). This is a classic magmatic zonation.
- calco-sodic palagioclase (darker minerals)
- titanomagnetite (very bright beacuse high iron content). If you zoom on the magnetites you will see tiny lamellae of ilmenite (exsolution). Can see it easily on the large grain at the upper centerof the image.
- the "crust" is a desert varnish. It has no bubbles.
- Some pyroxnes have been weathered and transformed into chlorite probably (choritization). Shown by darker areas with "cracks" in the pyroxenes. Especially on the left close to the "crust"
Das hohe-Auflösung SEM Foto findet ihr hier (1860kB):
http://www.asteroidchippings.com/Forum/SEM_backscatter_mode.jpgAuch wenn es nicht das gehoffte Resultat gab, war es für mich eine schöne Erfahrung, und habe ich wieder viel gelernt. Und das vor allem dank Jérôme Gattacceca, ein Wissenschaftler der die Zeit nimmt ein Laie wie mich zu „unterrichten“.
Schönes Wochenende!
Rob
Thema: Was könnte das sein??? (Gelesen 3068 mal)
