Module 2: Using the Petrographic Microscope
2.2 Thin Sections
Elizabeth A. Johnson; Juhong Christie Liu; and Mark Peale
- Describe the parts of a standard thin section.
- Describe the differences between a standard petrographic thin section, a thin section prepared for electron or ion microbeam analyses, and a thick section.
- Describe the steps necessary to produce a standard thin section, in the correct order.
Figure 2.2.1. A thin section on a petrographic microscope stage.
The general procedure for creating thin sections has remained nearly the same since the modern version was created nearly 200 years ago. In this section, we review examples of modern thin section making procedures.
Figure 2.2.2. Interactive diagram showing different types of thin sections.
Question 2.2.2 An electron microprobe determines the composition of a mineral in thin section by comparing X-rays generated from a beam of electrons hitting the atoms within the mineral to a set of compositional standards. What is the difference between a “microprobe” thin section and a standard thin section, and why do you think this difference is necessary?
Question 2.2.3 Thick sections are prepared for special analyses, such as fluid inclusion work (https://en.wikipedia.org/wiki/Fluid_inclusion) or FTIR spectroscopic analyses which is sensitive to epoxy and glass, so the rock section must be removable from the glass and glue. How is a thick section different from a standard thin section?
How are Thin Sections Made?
Preparation in a University Lab:
Use Hirsch, Dave (2012; Ret. 11/21/2018) How to make a thin section. https://davehirsch.com/other/thinsections/ to answer these questions:
Question 2.2.4 What do you do to a glass slide to “frost” it?
Question 2.2.5 What is a rock chip?
Question 2.2.6 Why do the instructions say to grind one corner off the glass slide?
Question 2.2.7 What should you do to the rock before you cut a slab out of it?
Professional Preparation: Watch these videos from Spectrum Petrographics, a professional thin section and petrography company, about how they create thin sections:
Question 2.2.9 Why does Spectrum Petrographics put quartz grains in the rim of each thin section billet?
Question 2.2.10 How does Spectrum Petrographics label the glass slides?
Question 2.2.11 Approximately how thick is the section after it is initially cut in the cutoff saw?
Additional Resources for Learning to Make Thin Sections
If you are interested in more detailed descriptions of the thin section equipment and steps to make thin sections, please see the following resources:
- Analytical Methods in Geosciences chapter on thin section preparation: https://courses.lumenlearning.com/labmethods/chapter/equipment_thin_section_preparation/
- Video playlist on YouTube showing detailed thin section procedures in laboratories at James Madison University and Northern Virginia Community College: https://www.youtube.com/playlist?list=PLc1yUU5DczrXJU5YL4mael1uDeST0vwtS