Geologists use a special microscope - called a petrological microscope - to look at these slides. By inserting polarisers into the incoming and outgoing light, the minerals that constitute the rock can be easily identified. However, the polarisers have a secondary effect - turning the slides into stunning works of art.
Kilchoan Learning Centre all about our local volcano.
Now Rob has taken his enthusiasm on-line by starting a blog - and, being a bit technical himself, some of the add-one he's using are great fun as well as enabling him to explain what are otherwise quite complicated ideas. Have a look at the blog entry here.
His blog is at http://geosec-rob.blogspot.co.uk/
Many thanks to Rob for the slide photos