Thin Sections- An Overview

Thin Section (in cross polarized) of Tremolite and Cummingtonte

If you’ve taken a higher level Geology course like Mineralogy or Sediments and Stratigraphy you may have some experience with thin sections of minerals and rocks. Love them or hate them you have to admit they are very interesting and can be fun if you don’t have to do assignments on them.

A thin section of a rock is just a very thin slice of a particular rock, usually 30 microns, in order to view different optical properties of various rock types and mainly different minerals. You see different minerals may look different in hand sample but under a petrographic microscope (ours can go 400x magnification) you can see some major differences. Some major features to observe when looking at a thin section and ones that I’ll go over in more detail later are; pleochroism, anisotropic/isotropic, interference colors (birefringence/retardation), and twinning.

As you can see by my pictures, thin sections can show very colorful and interesting pictures. Who would have thought rocks and minerals could look so cool. This is what I meant by thin sections could be fun. While I was studying thin sections for my exam in mineralogy it wasn’t too bad as I could see these pretty colors and crazy shapes and as another professor of mine said, “It’s trippy man!”.