Thinner Thin Sections

The canonical thickness for thin sections is 0.03mm. Professionals depend on it. Collectors insist on it. Still, if we have to rely on a conventional light microscope there are some times when thinner sections show more features. The dark, fine grained matrix of low petrographic type carbonaceous chondrites can hide smaller mineral grains. Polish off some of that material and more shine through. Two Tagish Lake C2-ung slides and two CH3 slides illustrate this.

Let’s call these two thin section samples Tagish Thick and Tagish Thin. The field of view is the same for each, 15 mm high. We are looking at them with light coming from the back.
Thin, of course, passes more light. It is thinnest at the lower right.

 

Tagish Thick up close and in cross polarized light. We see typical interference colors telling us that the section is at the correct thickness. Field of view is 3 mm wide.

 

Same view in plane polarized light.

 

Tagish Thin up close and in cross polarized light. No third order interference colors. The sample is thin. Field of view is 3 mm wide.

 

Same view in plane polarized light. Scads of detail.

 

Side by side comparison, Thick (correct, actually) and Thin.

 

These are “thick” and thin thin sections of NWA 4781 CH3. The field of view is the same for each, 30 mm wide by 20 mm high. Again, we are holding them up to the light.

 

The thicker CH3 in XPL and in PPL. FOV is 3 mm wide.

 

The thinner CH3 in XPL and in PPL. FOV is 3 mm wide.

 

Comparing the left sides of each PPL shot. The thicker (correct thickness) on the left and the thinner on the right.

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About the Author

John Kashuba
John is a natural history enthusiast living in Oregon.
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