Assignment of part 3: Thin section microscopy

Microscope

A foremost way to explore processes that have led to the formation of a rock as we observe it, is just looking at the rock at a larger magnification, i.e. by using a microscope. Quite a number of different microscope types exist - from simple instruments that magnify just a couple of times to super fancy instruments which enable to visualize individual atoms. As a rule instrument time on high-end microscopes, for example a transmission electron microscope, is 'not cheap' so to say. Therefore, to optimize your precious time on such an instrument the strategy is 'to know what you look at' at a low magnification so that no time is wasted on the expensive instrument for low-level exploration of the material.

For this first round of analysis, classical transmittent and reflected light microscopes are commonly used by earth scientists and material scientists. We are going to use transmittent light microscopes. By making thin sections of 30 micrometer thick of a rock specimen and polishing both surfaces we can see through the rock and determine constituent minerals, their grain size, preferential orientation, presence of pore space, deformation structures and many other items in that rock. Having a good overview of your rock under study is an important first step to solving your research question.

Rock collection

We are going to focus on crystalline rocks. The rocks have comparatively large grain sizes which serves as a good starting point for novice microscopists.

Your task

A manual describing the basic features of a transmittent light microscope will be available. In the manual there are sets of questions which guide you through the principles of thin section analysis. In class, the instructor distributes the thin sections for analysis.