An Article In Meteorite-Times Magazine
by Tom Phillips and Norbert Classen


D'Orbigny

Angrites are simply beautiful on the scope and D'Orbigny is up there with the best. This slide with was a loan to me from Jeff Hodges. He is also an excellent microscopist and has a micrograph gallery at http://www.meteoritethinsectiongallery.com/Alphaindex.html Once you go there, don't forget to come back!

Norbert Classen, once again, just happens to have a slice of this meteorite and he has been helping me with the content of my articles. He is providing the interesting part, I just take the close ups.

This is Norbert slice. He sent me a list of his planetary and achondrite meteorites and to say it is extensive is an understatement. I needed a new hard drive just to down load the names!


Norbert Classen:

"D'Orbigny belongs to the ultra-rare group of angrites, and with a TKW of 16.55 kg it's the largest member of this clan of achondrites which has ever been discovered. One oriented stone was found in a corn field near Buenos Aires, Argentina, after a farmer hit it with a plow in July 1979. In what might be considered a "barbaric act" by some the entire stone was crushed by classifying scientist Gero Kurat from the NHM Vienna.

My own small collection sample, a 0.846g slice with dimensions of 12x13x2mm, shows the typical features of this neat angrite: the sub-ophitic texture with laths of plagioclase, subhedral to euhedral augite and anhedral to subhedral olivine plus one of these remarkable round vugs and black ultrabasic glass filling pore spaces."



What a cool slice!

These are some images of skeletal crystal structures found in D'Orbigny.

Norbert was able to run these shots by Dr. Otto to help us understand what is going on in them.

Dr. Jürgen Otto's comments (translated from German to English).

"The central objects in the first, third, and fourth picture are zonar olivines with idiomorphic, rhombic crystall cores and clearly defined edges. In picture 1 and 4 the cores show yellow to red colors while the edges appear in blue to bluegreen polarisation colors; in picture 3 the core appears blue to green, the edge light green to yellow. This difference in appearance is due to the distinct crystallographic orientation of the olivine crystals in the thin section. The zonar distribution of colors indicates differences in chemism, especially regarding Fe, Ca and Mn contents. The second picture shows inclusions within a olivine core that could possibly represent kirschsteinite, a type of 'Ca-olivine' that is often found in angrites."

Here are a few more crystal shots.


This set is taken with a field of view (FOV) of 4.40mm. The shots break down like this:

1: plane polarized light
2: partially cross polarized light (-90 degrees)
3: fully cross polarized light
4: fully cross polarized light with a 1/4 wave retardation plate + 45 degrees
5: fully cross polarized light with a 1/4 wave retardation plate - 45 degrees


1: plane polarized light


2: partially cross polarized light (-90 degrees)


3: fully cross polarized light


4: fully cross polarized light with a 1/4 wave retardation plate + 45 degrees


5: fully cross polarized light with a 1/4 wave retardation plate - 45 degrees


This set is taken with a FOV=0.62 mm with the addition of a wave plate.


And next FOV= 0.40 mm.


Bringing it in just a little closer. FOV=0.25 mm.


Finally, getting right up close with a FOV=0.16 mm. This is the first time I have tried this. It is a high magnification series of polarization variations.

Once again:

1: plane polarized light
2: partially cross polarized light (-90 degrees)
3: fully cross polarized light
4: fully cross polarized light with a 1/4 wave retardation plate + 45 degrees
5: fully cross polarized light with a 1/4 wave retardation plate - 45 degrees


1: plane polarized light


2: partially cross polarized light (-90 degrees)


3: fully cross polarized light


4: fully cross polarized light with a 1/4 wave retardation plate + 45 degrees


5: fully cross polarized light with a 1/4 wave retardation plate - 45 degrees


I can never get tired of looking at angrites. For more to feed your D'Orbigny needs check out Jeff Kuyken's site http://www.meteorites.com.au/features/d'orbigny.html You will be amazed!


Be sure to visit Norbert Classen's site at:

Planetary Meteorites

 

Tom Phillips can be reached by email at:
STARSANDSCOPES@aol.com

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