Quartz Varieties

The quartz variety in the center is rose quartz. Clockwise from the upper left is crystal quartz, amethyst, citrine, and smoky quartz. The chemical formula for all of them is SiO₂, silicon dioxide. Trace impurities create the color in amethyst, citrine, and rose quartz. Free electrons caused by exposure to radiation create smoky quartz. Microscopic fragments of all of these varieties look the same under the microscope.