2 Minerals and the microscope

Although modern Earth Sciences departments use expensive and sophisticated electronic equipment to study minerals and rocks, the polarising microscope (which was the height of instrumental sophistication in the later 19th and early 20th centuries) remains an important tool in petrology (the study of rocks). This section gives an overview of crystal optics, a basic understanding of which is essential for use of the polarising microscope in petrography (the description of rocks). By identifying minerals and examining their interrelationships, petrographic evidence can be used to identify rocks and deduce how they formed.