Tragically, very few people own a polarising microscope. The proportion of the world’s population with regular access to a polarising microscope is also distressingly tiny. Most schools – even those that teach geology as a subject – cannot afford enough microscopes to run practical petrography classes. Even some universities struggle to deliver petrography practicals to large student cohorts. And then a global pandemic turns practical teaching upside-down …

Lucky for us that there is the Virtual Microscope (VM) ready to help, in all those situations and many more!

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 nineteenth 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.  Our VM offers the option of a more blended approach to teaching and assessment, supporting practical lab classes; it is also a great revision aid.

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 is based on material from an Open University geology course that you can study as part of several OU Science qualifications.

Links to other great petrology sites

Alessandro Da Mommio's Alex Strekeisen website features loads of high-quality petrology images and stacks of interesting info.

Optical Mineralogy - a free online reference book packed with mineral descriptions and images, intended as a practical aid for students observing minerals with a petrographic microscope. Lovingly crafted by Dexter Perkins, Matt Kohn and John Brady, this site features numerous beautiful images of minerals that can be toggled between PPL and XPL with a minimal mouse roll. The authors have focused on providing practical tips on how to identify minerals and distinguish them from each other.

See the Virtual Microscope's own Andy Tindle on his Pegmatite site.

Imperial College's great rock library with lots of images and background information was recently the victim of a cyber attack. They are now seeking funds to upgrade their hosting.

Frank Mazdab’s impressive rockPTX site, which offers numerous videos and superimposed PPL/XPL images revealed using a slider.

A brilliant site for conveying the thrills and the pitfalls of hunting for meteorites is Svend Buhl's Meteorite Recon. He tells the stories of desert expeditions engagingly and the site is littered with high-quality, striking images. The stunning banner image for our EUROPLANET Meteorites Collection is used with Svend's kind permission.