she saw fit to spend all of her time studying the stones , which was not an easy task because the rocks could n't be chipped to obtain smaller samples and the light of the microscope made them jump and disappear at the least convenient moment , leaving the frustrated sister with the task of searching for them throughout the lab , under tables , in cupboards , on top of shelving units , next to the sink , while the surreal minerals changed color and pattern thus becoming even harder to find .