An Article In Meteorite-Times Magazine
by Tom Phillips and Martin Horejsi
We all have seen meteorite thin sections photographed in cross polarized light (Xpol). The colors can be beautiful, but to most, (my self included) it's just that. Beautiful images.
I won't try to explain how colors are changed in Xpol pass through light. What I am talking about in this piece is Xpol used in examination of unprepared hand samples. The effect is stunning. No color alteration, instead, it seems as if you are looking right into the rock. Kind of like Super Man X-ray vision.
The results are best when combined with a stereo microscope of modest magnification, say 7-15 X, but are also useful with no magnification.
An example of a fiber optic ring light with polarizers attached. The outer ring is a polarizing filter that the light is projected to the subject though. The returning light, reflected off the subject, passes through a central polarizer. The first photo is this setup attached to a stereo microscope.
The above photo shows a handy method of using Xpol. It can also be used quite nicely held in the hand and not necessarily attached to a microscope. There are lots of ways to accomplish Xpol viewing and not all are very expensive. I have worn Polaroid sunglasses while examining meteorites illuminated by a desk lamp with a camera polarizing filter taped on the front. (It worked!) Just experiment, you will have fun and be amazed.
For those out there with a Stereo microscope who have not set it up with Xpol, perhaps these images will win you over. Please keep in mind, I am showing the technique, and not my skill at taking micrographs through the eyepiece of an inexpensive scope. I pride me self on the micrographs I produce with very different equipment.
Test samples. These two meteorites are our subjects. Lets say we are wondering if they are worth cutting into or, maybe, we are thinking about buying them and can't cut them first.
The following are before and after pairs of micrographs. Without and then with Xpol. Larger 52 gr. rock on left.
This is a micrograph taken with no polarizers at a magnification of 15X. Not many details are visible. Just the surface.
This is the sample illuminated with Xpol. Notice the increase in visible details.
I found the first sample to contain a lot of chondrules, perhaps it is worth looking into, but the second sample looks like it might be a Urelite? I think I'll cut that one and get it on the Neophot. If I were examining them for a purchase, I would take them both.
To me, Xpol light is more important than the microscope in examining meteorites. Feel free to email me if you are setting up your scope and want ideas. I have set up many. Hint: If you want to go cheap! Hit the thrift stores for camera polarizing filters.
Tom Phillips can be reached by email at:
The Tom Phillips Microscopic Meteorite Photography and Gallery