Photograph 2. Typical textural view in polarized light showing most of the features of this rock. The coloured crystals at the bottom are olivine, those across the top are calcic pyroxene and the grey striped crystals are twinned plagioclase feldspar. Importantly, the dark greyish minerals in the centre are feldspathoids and zeolites which are reactive to acidic substances. Scale: side of photograph is 1.6mm