Cochise College        Student Presentation

                          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. 


Text Box: This is an example of zoning.  This is feldspar in lava.


Text Box: This is an example of twinning.  They are crystals of pyroxene.






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.