This week I decided to share a few more pictures from the thin section I wrote about last week. Unfortunately, I can’t give any great detail about what you’re seeing because, quite frankly, I myself am not sure what I’m looking at. Identifying minerals in meteorites is a whole different beast then that of volcanic and metamorphic rocks. To be sure, there is plenty of mafic minerals: mostly olivines and augites. At this point in my work at the meteorite lab, I’m learning more about the visual classification of meteorites. Are there plenty of well defined chondrules and glass? Then you probably have an LL3 (low iron, low metal). No chondrules and a fairly homogenous texture? Chances are it’s an L6, or if someone is feeling courageous, it could possibly be classified as an L7.
Plane light view of interesting "bleb" wedge (for lack of a better word)
Here's the same view, but in crossed polarized light. Notice the difference in detail?
The plane light view doesn’t tell us too much, but when we go into the crossed polarized image, a few things become apparent. That interesting wedge really stands out from the rest of the sample. My initial impression of the grey/blue part was that it was some sort of melt that had cooled, kinda of like a glass. The only problem with that assumption was that glass goes black under cross polarized light. Alex Ruzicka, one of the professors that runs the lab, guesses that it could be plagioclase or even a phosphate. I get the feeling it’s something we won’t really know till we’ve done some SEM work on it.
This next image is of the same area, but a higher magnification. Those minerals studded in the grey-blue mass are mafic in origin. My guess is that the minerals with the higher birefringence (the pretty, colorful ones) are olivines and that the large whitish ones are probably a pyroxene.
A cross polar image of the same area, magnified 10x.
What I find really fascinating about this meteorite is that it’s brecciated. Each of it’s individual pieces record a different thermal history, and the lack of visible chondrules possibly indicates that each piece has gone through a high of metamorphism. I hope to understand the process more as I continue my lab work and studies.
A large phenocryst- possibly an olivine.
Glacial Till 