Getting Started with Cross Polarized Light
By Tom Phillips

I am not a professional in the field of either meteorites or microscopes and as such I have a huge degree of flexibility in chasing down what looks "COOL" without always being entirely able to explain myself. Every time I sit down to a microscope I am amazed, surprised and at times confused.

The first time I tried to view a meteorite thin section was an embarrassing event. I had out my son's toy store microscope and I wanted to see colors. I had heard that polarized light was needed so I put on a pair of polarized sunglasses and held another pair over the microscope's light bulb. It was awful, dark and impossible to focus but I saw "colors".

This is an attempt to show how fun, interesting and easy viewing meteorites in cross polarized (Xpol) light can be. Now saying this is easy is like saying that getting a telescope and looking at the stars is easy. It is, but you wouldn't consider an astronomer's job as "easy work" The same goes here. There are people who have dedicated a great deal of time to Xpol analysis and it can be very complicated. This field is essential to the science of meteorite collecting. In fact, the roots of our meteorite classification system is inter grown with the use of polarizing microscopes.

A friend brought over an Olympus BH (this is a typical biology student microscope) and in less than a half hour we were looking at beautiful colorful images. I buy old camera polarizing filters where ever I find them. One of these filters was placed over the illuminator (light source). We found one that fits so it's easy to rotate without falling off. The next step was to take off the microscope's head and measure for the second filter. It has to fit down in and allow the head to be put back on with it still in place. I found a nickel was about the right size. I traced the size onto another filter using a permanent marker and cut it out.

If you collect meteorites you probably have or know someone with a diamond rock saw. A tile wet saw will do. Cut the filter into an approximate size square and shape into the correct size using the side of the saw blade. It's not as hard as it sounds and you don't need to be perfect.

With these filters in place, all you need is the thin section. Thin section quality can vary greatly so remember, One good thin is worth a drawer full of junk.

If you happen to have a microscope capable of combining transmitted and incident light (Unfortunately, most are not), you are already aware of the difficulties involved in getting a good well balanced photograph. Controlling the light so one light source doesn't over power the other without closing down diaphragms to the point it effects focus and contrast, is almost impossible. Here is a trick I found to work well. Put two polarizing filters in the incident light source path (Yes, both before the sample). Rotate theses two filters independently of each other. This will control how much light gets through without touching the diaphragms.

Look at the images in the gallery and it will give you an idea of what you will see. Keep in mind, photos cannot do it justice. Seeing it in person is unbelievable. I've even heard it said "The colors are so beautiful they will make you weep."   The possibility of discovery is still left. Even for the average hobbyist with modest equipment. These rocks came from who knows where in space, so remember, "There is no such thing as an Ordinary chondrite". (I heard that some where and I wish I remembered who said it)