Fluorite and Quartz can be purple, with purple quartz known more commonly as amethyst. This leads us to the next step in mineral identification, crystal form . Allochromatic minerals get their colors from impurities rather than elements basic to the minerals' compositions. An example would be rose quartz, which gets its pink color from titanium and iron. A mineral's plane of mechanical fracture.
Idiochromatic minerals get their colors from elements basic to the minerals' compositions.
An example would be dioptase which gets its green color from copper. A thin sheet, plate, or scale of material. The property exhibited by minerals of showing different colors when transmitted light is viewed along different axes.