This is a specimen of primarily colourless lustrous barite crystals (which is the only mineral species that was on the label). However, under the microscope, pale blue turquoise can be seen, and an isolated tarnished chalcopyrite crystal (not in the photo).
When I took a close-up photo, I could then see tiny yellow crystals, not picked up under the microscope until after I knew they were there. These are very, very, very small, only about 0.006mm across! At this magnification, it is difficult to identify the mineral species, however they do look very much like smaller versions of crystals that have been analysed, and shown to be mottramite.