What are the best practices for preparing thin sections for optical and electron microscopy?

1 Choose the right sample

The first step in preparing thin sections is to select a representative sample of the rock or mineral of interest. You should consider the size, shape, orientation, and preservation of the sample, as well as the research question and the type of microscopy you plan to use. Ideally, the sample should be large enough to fit on a standard slide (26 x 46 mm), have a regular shape (preferably rectangular or square), and show the deformation features and microstructures that you want to analyze. You should also avoid samples that are too fractured, weathered, altered, or contaminated.

2 Cut and trim the sample

The next step is to cut and trim the sample to fit on the slide and remove any excess material. You can use a rock saw, a diamond blade, or a wire saw to cut the sample, depending on its hardness and brittleness. You should also mark the orientation of the sample, such as the top, bottom, north, south, east, or west, using a permanent marker or a label. This will help you later to correlate the thin section with the field or laboratory data. You should then trim the sample to a thickness of about 1-2 mm, using a grinder or a lapidary machine. Be careful not to overheat or damage the sample during this process.

3 Mount and polish the sample

The third step is to mount and polish the sample on the glass slide. You can use different types of adhesives, such as epoxy resin, Canada balsam, or acrylic cement, depending on the type of microscopy you intend to use. You should apply a thin and even layer of adhesive on the slide and the sample, and press them together firmly. You should then let the adhesive cure for at least 24 hours, or according to the manufacturer's instructions. After that, you should polish the sample to a final thickness of 30 microns, using a series of abrasive papers or discs, from coarse to fine. You should check the thickness of the sample regularly, using a micrometer or a caliper, and avoid overpolishing or underpolishing the sample.

4 Clean and cover the sample

The fourth step is to clean and cover the sample to protect it from dust, scratches, and moisture. You can use a soft cloth, a brush, or compressed air to remove any debris or residue from the sample and the slide. You should then cover the sample with a thin glass cover slip, using a drop of adhesive or a mounting medium, such as Canada balsam or epoxy resin. You should align the cover slip with the edges of the slide and press it gently to remove any air bubbles or excess adhesive. You should then let the cover slip dry for at least 24 hours, or according to the manufacturer's instructions.

5 Label and store the sample

The fifth step is to label and store the sample properly. You should use a permanent marker or a label maker to write the name, number, location, orientation, and date of the sample on the slide. You should also include any relevant information, such as the type of rock, mineral, deformation mechanism, or microstructure that you want to study. You should then store the sample in a suitable container, such as a slide box, a slide holder, or a slide envelope. You should keep the sample away from heat, light, moisture, and chemicals, and handle it with care.

6 Analyze the sample

The final step is to analyze the sample using optical or electron microscopy. You can use different types of microscopes, such as polarizing microscopes, scanning electron microscopes, or transmission electron microscopes, depending on your research question and the level of detail you need. You should follow the instructions and protocols of the microscope you use, and adjust the settings and parameters accordingly. You should also take notes, sketches, photographs, or measurements of the sample, and interpret the results in relation to the structural geology concepts and theories.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?