Professor Dave Prior
Light microscopy is actually a really beautiful tool for rocks and minerals because rocks and minerals have specific optical properties, which means that we can distinguish the different mineral types very easily using nothing more sophisticated than an optical microscope with polarising filters in it. We look at what we call microstructures as well – the arrangement of those minerals. So a rock which has been deformed in the earthquake process will have lots of angular bits and fractures in it whereas a rock which has been deformed at higher temperature and has not undergone fracturing, then the grains will have elongate shapes, for example, so it might have been an original spherical grain and it gets pulled out to make a long thin thing. So we look at that first on the optical microscope, and the microscope enables us to look at features on a scale where we could also see the features by looking with our eye and go up magnification to a scale where we can see features which we’ll then recognise when we get to the scanning electron microscope. We can do a huge amount with an optical microscope, and it’s fast, it’s cheap, it’s easy to apply. It generates scientific information in its own right and it’s also an essential screening process for the samples which we’re going to use for more detailed types of analysis.
Professor David Prior and Dr Virginia Toy, Department of Geology, University of Otago.
Rock micrographs courtesy of Dr Virginia Toy, University of Otago.