The conventional classroom visual aids for teaching about minerals and rocks are either flat images (photographs, often digital images viewed online) or hand specimens of rocks and minerals. University teaching might include access to thin sections and polarising microscopes. Teaching about geology with visual aids such as photographs doesn't require direct access to the sort of rock collections found in museums or in university collections, but such images are flat and static and not an ideal way to develop mineral identification and classification skills. Rock hand specimens and thin sections are the best approach to developing key skills but not everyone has access to teaching laboratories equipped with polarising microscopes, and even when microscopes are available, access time is often limited by lab times or the need for microscope sharing.
In the mid-1990s The Open University began to tackle this problem by developing a digital polarising microscope, which featured a box of electronic slides that could be viewed as a simple rotating view. The first virtual microscope contained twelve thin sections of common igneous and metamorphic rocks. They could be viewed with an electronic hand lens or with the virtual microscope itself. Each thin section could be rotated in plane polarised light or between crossed polars, and then to assist students even further both types of lighting could be observed simultaneously.
Virtual microscopy has progressed since then and the first pilot of the new generation of Open University virtual microscopes was produced in 2008. The new 'VM', as it became known, delivered high resolution microscope images via an internet browser on most types of computer and operating system without the need for additional software or a high power computer. The system was developed for Open University courses and students first used it in 2010.
Since then geology students have been able to study rock thin sections in detail as if they were using a physical microscope: by zooming in and out, and viewing in plane polarised light and between crossed polars. Furthermore, because the images are digital, the virtual microscope has additional capabilities beyond those available with a basic polarising microscope, such as measurement, XY location, and social networking technologies that provide opportunities to create student communities and shared experiences. While virtual microscopes don't replace physical microscopes, they are a significant step change that allows students to explore whole thin sections either supervised, on their own, or with other students, and have a learning experience much closer to conventional laboratory microscopes.
If you would like to know more about the features you see in the virtual microscope, or how geologists identify and classify rocks and minerals, there are lots of resources available.