This module provides an overview of equipment used for thin section preparation, including manual polishing techniques.  If you have completed readings and watched videos in section 2.4, you may already recognize the equipment described here.

This module also describes the procedures and specific operation of the equipment at two schools (JMU and NVCC) in a series of videos.  Even if you are not a student at either of these schools, these videos provide practical tips for operating the machinery and creating a thin section.

Learning Objectives

• Explain the purpose and function of each piece of equipment used to prepare thin sections.
• Describe the specific steps used at two schools (JMU and NVCC) to create thin sections.

Prior Knowledge and Skills

• 2.2 Thin section and thick section anatomy (recommended)
• 2.3 History of thin section preparation (recommended)
• 2.4 Procedure: how to make a thin section 

Key Terms

• Rock saw
• Cutoff saw
• Grinding wheel
• Micrometer

2.5A Rock Saw and Cutoff Saw at JMU

Watch these videos about rock saws:

AMiGEO (4/6/2018) Thin Sections: Lab Safety. https://youtu.be/0_isoNgBmOQ

AMiGEO (4/6/2018) Thin Sections: Anatomy of a Rock Saw. https://youtu.be/KrIUEIdP2sY

AMiGEO (11/27/2018) Thin Sections: Cutting a Rock. https://youtu.be/uKiPu4fD_8k

AMiGEO (11/27/2018) Thin Sections: Cleaning up the Rock Saw. https://youtu.be/RPfhmXPiNg0

AMiGEO (11/27/2018) Thin Sections: Parts of a Cutoff Saw. https://youtu.be/W1-Hoad43Nw

AMiGEO (11/27/2018) Thin Sections: Cutoff Saw Blade Sharpening. https://youtu.be/lXrxRlw0lw0

Guided Inquiry

2.5.1 What safety equipment should you wear in the rock saw lab?

2.5.2 Why is it necessary to use water in the rock saws?

2.5.3 What could happen if you twist the rock while you are cutting it on the rock saw?

2.5.4 What are three things you should do to clean up the rock saw after you use it?

2.5.5 How is the thin section cutoff saw similar to the rock saw?  How is it different?

2.5.6 How is a diamond rock saw blade different from a regular saw blade (like one you might use to cut wood)? How is it “sharpened?”

2.5B Grinding wheels

Watch these videos about the JMU grinding wheels:

AMiGEO (4/6/2018) Thin Sections: Vertical Spindle Grinding Wheel Part I. https://youtu.be/wlnjl6Kydbo

AMiGEO (4/6/2018) Thin Sections: Vertical Spindle Grinding Wheel Part 2. https://youtu.be/eZZPcqL5Kak

AMiGEO (8/16/2021) Thin Sections: Polishing Wheel. https://youtu.be/QyYwIVnMNtg 

AMiGEO (4/6/2018) Thin Sections: How To Frost Thin Section Slides. https://youtu.be/GxzcI1cKh48

(Please note: this step is not necessary if using Norland UV Epoxy.)

Guided Inquiry

2.5.7 What is the purpose of the vertical spindle grinding wheel?

2.5.8 What are two differences between a vertical spindle wheel grinder and a horizontal spindle wheel grinder like the one on our thin section grinder used for frosting slides?

2.5C Manual polishing

Watch these videos about polishing:

AMiGEO (4/6/2018) Thin Sections: How To Polish Rocks on a Glass Plate. https://youtu.be/SSpteu6aUPE

AMiGEO (4/6/2018) Thin Sections: Evaluating the Quality of a Polished Surface. https://youtu.be/eOgtBZg0XWQ

The grit size of a polishing grit or sandpaper refers to the size of the particles in the grinding material. This table shows the relationship between grit designation number (CAMI) and  the average particle diameter in micrometers: https://en.wikipedia.org/wiki/Sandpaper#Grit_size_table

Guided Inquiry

2.5.9 Someone polishes with 30 micrometer grit, then 1 micrometer grit, and finally with 15 micrometer grit.  Are they doing it in the right order? Why or why not?

2.5.10 Should you press down hard while manually polishing?  What is the best technique?

2.5.11 After using each grit, what should you do before going to a different grit size?

2.5D Digital Micrometer

The figure below shows the parts of a digital micrometer, which is used to measure relative thicknesses.

Watch this video about measuring thickness on a digital micrometer:

AMiGEO (4/30/2018) FTIR: Using the Digital Micrometer. https://youtu.be/cOZLevWtP90

Guided Inquiry

2.5.12 A digital micrometer can help you measure thickness of your thin section as you polish the final surface.  What is the limit to the usefulness of the micrometer for this purpose?

2.5E Labeling

Keeping track of your samples is very important.  It can be difficult to determine the origin of a thin section unless you properly label the rock chip or blank, as well as the thin section, during the thin section making process.

Watch these videos about labeling:

AMiGEO (5/19/2017) Thin Sections: Labeling Rock Blanks. https://youtu.be/ZRjTPtWHfj4

AMiGEO (4/6/2018) Thin Sections: Labeling Frosted Slides. https://youtu.be/lTBneFG42qs

AMiGEO (6/15/2017) Thin Sections ft. Spectrum Petrographics: Behind the Scenes. (at 4:57) https://youtu.be/Kjry4Q-qMe0?t=297

(Please follow the link above- the embed is not working)

Guided Inquiry

2.5.13 At JMU we write on our slides using a Tungsten Carbide or Carbide Tipped Scriber pen for glass, which cost about $4 at the local hardware store.  Why don’t we use a laser engraver?

2.5F Epoxy

Watch the epoxy procedure from Northern Virginia Community College:

AMiGEO (July 9, 2019) Making Rock Thin-Sections: 06/10 – Epoxying Slides. https://youtu.be/g1HXBpyfkQ0

Not all epoxies are two-part mixes like the one above.  In recent years at JMU, we have successfully used a UV-curing epoxy called Norland Optical Adhesive.  This epoxy is mounted onto the thin section chip as described above, but it is cured by placing it under a longwave UV light for about 10 minutes, then in a heated cabinet kept at 50°C for at least 12 hours.

Thin Section Procedure: Start to Finish

A thin section procedure from Northern Virginia Community College is recorded step by step in this YouTube playlist:

https://www.youtube.com/watch?v=tA1XqcF7wPk&list=PLc1yUU5DczrWuIwk44UERgSx6xqszeE0n

Concept Checks

Concept Check 2.5.1

Compare the equipment at JMU to the equipment described in the previous module for Spectrum Petrographics (2.4 Procedure: How to make a thin section).  What are some differences between the types of equipment used?

Concept Check 2.5.2

Compare the procedure at JMU to the procedure at NVCC.  How are the equipment and the steps similar, and how are they different?

Concept Check 2.5.3

Is it safe to put your finger on a rock saw blade?  Why or why not?

Summary

This module shows some of the techniques used in the JMU thin section lab, and also demonstrates use of our equipment.  There are more detailed descriptions of earlier versions of the same equipment in the historical resources in module 2.3 History of Thin Section Preparation, especially in: Johannsen, Albert (1918), Chapter XLI. Preparation of thin sections of rocks. Manual of petrographic methods, New York, McGraw-Hill Book Co.2d ed., p.572-60.

If you would like to delve even deeper into this topic, this book contains a large section describing thin sectioning equipment and how to set up a thin section laboratory, as well as preparation techniques: Allman, M., Lawrence, D.F. (1972) Geological Laboratory Techniques. Arco Pub. Co, New York, 355 p.

References

Allman, M., Lawrence, D.F. (1972) Geological Laboratory Techniques. Arco Pub. Co, New York, 355 p.

AMiGEO (4/6/2018) Thin Sections: Lab Safety. https://youtu.be/0_isoNgBmOQ

AMiGEO (4/6/2018) Thin Sections: Anatomy of a Rock Saw. https://youtu.be/KrIUEIdP2sY

AMiGEO (11/27/2018) Thin Sections: Cutting a Rock. https://youtu.be/uKiPu4fD_8k

AMiGEO (11/27/2018) Thin Sections: Cleaning up the Rock Saw. https://youtu.be/RPfhmXPiNg0

AMiGEO (11/27/2018) Thin Sections: Parts of a Cutoff Saw. https://youtu.be/W1-Hoad43Nw

AMiGEO (11/27/2018) Thin Sections: Cutoff Saw Blade Sharpening. https://youtu.be/lXrxRlw0lw0

AMiGEO (4/6/2018) Thin Sections: Vertical Spindle Grinding Wheel Part I. https://youtu.be/wlnjl6Kydbo

AMiGEO (4/6/2018) Thin Sections: Vertical Spindle Grinding Wheel Part 2. https://youtu.be/eZZPcqL5Kak

AMiGEO (5/19/2017) Thin Sections: Finishing Grinding Wheel. https://youtu.be/GopO7v9t_3s

AMiGEO (4/6/2018) Thin Sections: Plumbing for the Finishing Grinding Wheel. https://youtu.be/w7Co2NRX2as

AMiGEO (4/6/2018) Thin Sections: How To Frost Thin Section Slides. https://youtu.be/GxzcI1cKh48

AMiGEO (4/6/2018) Thin Sections: How To Polish Rocks on a Glass Plate. https://youtu.be/SSpteu6aUPE

AMiGEO (4/6/2018) Thin Sections: Evaluating the Quality of a Polished Surface. https://youtu.be/eOgtBZg0XWQ

Wikipedia contributors. (11/6/2018). Sandpaper. In Wikipedia, The Free Encyclopedia. Retrieved 15:28, November 30, 2018, from https://en.wikipedia.org/w/index.php?title=Sandpaper&oldid=867602684

AMiGEO (4/30/2018) FTIR: Using the Digital Micrometer. https://youtu.be/cOZLevWtP90

AMiGEO (5/19/2017) Thin Sections: Labeling Rock Blanks. https://youtu.be/ZRjTPtWHfj4

AMiGEO (4/6/2018) Thin Sections: Labeling Frosted Slides. https://youtu.be/lTBneFG42qs

AMiGEO (6/15/2017) Thin Sections ft. Spectrum Petrographics: Behind the Scenes. (at 4:57) https://youtu.be/Kjry4Q-qMe0?t=297

AMiGEO (July 9, 2019) Making Rock Thin-Sections: 06/10 – Epoxying Slides. https://youtu.be/g1HXBpyfkQ0

AMiGEO (1/10/2020) Thin Section Procedure: Northern Virginia Community College https://www.youtube.com/watch?v=tA1XqcF7wPk&list=PLc1yUU5DczrWuIwk44UERgSx6xqszeE0n 

Licenses and Attributions

Videos created by AMiGEO: CC-BY license.

Wikipedia page CC-SA license.

Figure created by Mark Peale, Elizabeth Johnson, and Juhong Christie Liu, JMU.

Text written by Elizabeth Johnson, JMU

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