An Article In Meteorite-Times Magazine
by Tom Phillips
NWA 2986 Shergottite
The material was provided by Jim Strope. http://www.catchafallingstar.com Jim provided the rock, Jeff Hodges had the thin made and I got to put it on the scope.
Naturally, Jeff and I wanted the thin section to turn out well. When we saw it for the first time we both were concerned that it had large areas of epoxy fill. There was so much clear glass to it. It wasn't in till after several hours on the scope that I was sure I was looking at Martian glass and not "fill". I have examined Martian thin sections before but I have never seen glass so window clean in any other.
I sent some shots to Dr. Irving and he was so cool! He took the time to provide an explanation of this glass. This is what he wrote.
"The clear glass is maskelynite, which is produced by shock transformation of plagioclase (labradorite) during ejection of most Martian meteorites (except nakhlites). It's called a diaplectic glass, and is formed not by melting but by shock distortion of the feldspar crystal structure to the point where it becomes amorphous and amazingly clear (limpid like distilled water). Thus it will not have any vesicles (just tiny inclusions of pigeonite, phosphates, oxides, etc. that were originally inside the plagioclase on Mars). However, elsewhere in the thin section there could be some cross-cutting dark, glassy shock veins that do contain vesicles (of trapped Martian air, which in other shergottites is the proof of Martian origin for all such rocks).
The following are some shots broken up in to magnification groups that show both the beautiful and the interesting. Which is to say. some of these images are ugly but still interesting enough to share!
These first 4 shots are viewed at a magnification of 100X in cross polarized transmitted light with the addition of a retardation wave plate. All images show the glass I was working with. Image #3 is nearly all Martian glass. At first I wasn't sure if I had moved off the meteorite and was just looking at the glass slide.
This set is viewed at a magnification of 160X using the same techniques. What looks like specks of rock scattered on the slide is actually mineral bits suspended in the glass!
This set is viewed at 160X as well but with the addition of incident (reflected) cross polarized light. This shows the detail of the opaque material next to the glass.
These 6 shots are taken on the Neophot in only incident (reflected) cross polarized light. These methods do not bring out the brilliant colors but they do reveal what the rock really looks like up close. The first 3 are at 345X and the next three are 700X.
The last set is 400X transmitted cross polarized light with a wave plate. I found the bright mineral colors set against the clear glass to be quite stunning. Small rotation of the wave plate changes the back ground color but rotation of the sample changes the colors of the mineral grains only. The glass does not change in rotation. It was hard to get used to!
Thanks Jim for providing the material for this thin section. What a great time I had examining it. With all the glass in this Martian it must be amazing in a large hand sample. Jim had said this one was special!
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