Options for Thin Section Preparation

Petrography is a complicated science. Rocks, minerals, and similar materials are very complex. Naturally, the science of analyzing them is as well. There are many petrographic processes that may be performed. These different processes sometimes require the samples to be prepared in different ways.

Thickness

The first variable to consider when ordering a sample is how thick you want it to be. Standard thin sections are 30 micrometers, but can be cut to different sizes if needed.

Dyes

Thin section samples are always impregnated with an epoxy or resin. The epoxy or resin fills the empty space in the rock or mineral. It’s then stained with a colored dye, often blue, which helps show how porous the material is. Additionally, fluorescent dye can be added to see the smaller pores in the sample.

Staining for Minerals

The sample can also be stained to show the presence of certain minerals. There are several minerals that samples are commonly stained for. One such mineral is calcite, which is frequently found in limestone. Whether the sample is stained for different minerals depends on a few factors. The composition of the rock plays a huge part. If the rock was largely made of limestone, the sample would likely be stained for calcite. Another factor is the goal of the analysis.

Covering

The final step of the preparation process is covering or polishing the sample. In the past, covering thin sections was more popular than polishing them. A cover would be glued onto the sample and that would be it. But, the cover interferes with many processes. Some petrographic processes work better with uncovered samples. Other processes are impossible with covered samples and must be performed on polished samples.

Polishing

Using a polished thin section has become more popular over time. Polishing the sample helps yield more accurate quantitative measurements. This is because there are fewer scratches and pits to get in the way of observations. For example, grain size is easier to observe without imperfections getting in the way. Polished samples are necessary of a microprobe is being used. The microprobe cannot properly analyze the composition of a covered sample.

When ordering a thin section, there are many factors to consider. You may want to be able to see even the smallest pores in the rock. Maybe you want to easily find the presence of certain minerals in the sample and need it to be stained accordingly. A polished thin section may be required for certain necessary processes. The goal of the analysis also influences what choices would be best.