The use of microscopes to study optical properties in order to identify crystals, the science known as petrology, was first developed in Sheffield by Henry Sorby in the late 19th century. Today petrology remains one of the key skills in geology, and most students learn to use polarising microscopes to study the optical properties of polished rock slices just 30 microns (0.03 mm) thick.
While the striking colours and intricate textures revealed by polarising microscopes are inherently beautiful, there is a great deal of geological information contained in those colours and textures. Learning to recognise, identify, and classify minerals and rocks under the microscope is a skill that takes a great deal of practice. Moreover, as with much of science-based learning, the practical skills of petrology are not primarily related to learning facts, but are actually concerned with learning how to discriminate and classify within the paradigms of the discipline. The problems of teaching with complex visual materials, in effect of teaching students 'how to see' from the scientific perspective, is thus a skill that can be taught using a virtual microscope.
If you want to learn more about studying thin sections of rocks why not try an introduction to studying rocks under the microscope on the OpenLearn website. This introduction comes from a geology course in the Open University Earth sciences pathway of the Natural Sciences BSc qualification.
LInks to other great petrology sites.
Imperial College have a great rock library with lots of images and background information
Andy Tindle's Pegmatite site
See also Alex Strekeisen's great website for lots of petrology images and info.