optical mineralogy
英[ˈɔptikəl ˌmɪnəˈrɔlədʒi:]美[ˈɑptɪkəl ˌmɪnəˈrɑlədʒi]
A [[petrographic microscope, which is an optical microscope fitted with cross-polarizing lenses, a conoscopic lens, and compensators (plates of anisotropic materials; gypsum plates and quartz wedges are common), for crystallographic analysis.]]