The process of making thin sections is fascinating, as we found out in Part 1, but things start to get really exciting when light passes through them. Especially if we use polarizing filters.

We can place a thin section on a microscope and get a pretty good look at it.

Or we can place it on an apparatus like the one IODP Imaging specialist Bill Crawford built. 

This has a camera mounted above it that is capable of taking some pretty impressive pictures.

What is even more amazing is what happens when we put polarizing filters on either side of the thin section.

The light travels up through one filter, then the thin section, and then continues up through the second polarizing filter. The light waves are aligned and they accentuate the different minerals present in the thin section.

When you spin the polarizing filters the minerals change colors. This helps geologists determine the make up of the rock.

For example, that gold looking crystal is a mineral called olivine. The blue crystals are clinopyroxene and the black and white crystals are plagioclaise feldspar.