Geology Home Page
Roger Weller, geology instructor
Creating Thin Sections
by Jill Forsythe
text equipment process chart samples references
Thin Sections Charts
This chart shows the crystals present in thin sections. The crystal is identified by the shape and color of the crystals. Certain crystals also have cleavages and twinning or zoning which helps in their identification.
This is a Birefringence Chart. This chart is made from a photograph of a crystal of quartz viewed between crossed polars. On the left side is the first order, ground to about 30 microns thickness. The chart shows the quartz crystal color changes as it gets to a thicker slide, up to about .15mm at the end. As you can tell there are more colors in the thicker slices. Half of the first order, on the left side, you can see the desired thickness shades from black to grey to white to yellows. Many rocks have quartz in them so you can use the quartz as a guide to see if your thin section is thin enough. When your section is thin enough and there are still colors in it they are indicators of other minerals present. For example, Olivine, if present in a section is almost a reddish color.